outboard for a Mac Classic D/S
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Sum,
Looking at your chart, I guess what I'm trying to say is for example: choose 9mph or so with an 8 inch prop at 2500 rpm over 9mph or so with a 6 inch prop and 3500 rpm. Seems frictional losses would be less at 2500rpm. Since we (at least us nearer sea level) don't need all the power available at rated rpm from a 10 hp motor.
I better get something done here at home even if its wrong. Talk to you guys later
Looking at your chart, I guess what I'm trying to say is for example: choose 9mph or so with an 8 inch prop at 2500 rpm over 9mph or so with a 6 inch prop and 3500 rpm. Seems frictional losses would be less at 2500rpm. Since we (at least us nearer sea level) don't need all the power available at rated rpm from a 10 hp motor.
I better get something done here at home even if its wrong. Talk to you guys later
Sumner, a little more info on the starter current. I ran the outboard in a tub of water today for maybe 20 minutes.
With the engine still warm and the safety switch off (wont start), the starter button was pushed for 5 seconds. Just on startup, the current jumped up to 41 amps but then soon went down to about 35 amps until the end of the button push. The starter also says ".5KW" which is ballpark with the 35 amps.
Seems like great outboard.
With the engine still warm and the safety switch off (wont start), the starter button was pushed for 5 seconds. Just on startup, the current jumped up to 41 amps but then soon went down to about 35 amps until the end of the button push. The starter also says ".5KW" which is ballpark with the 35 amps.
Seems like great outboard.
The article posted has the same mentality of picking a prop based on maximum thrust at some boat speed. Ie, they took a 9.9 outboard and got 5.7 mph with the standard prop but got 6 mph with a high thrust prop (I think the boat was a pontoon boat or something like that). In both cases, the outboard was probably run at max throttle to get these speeds and probably had higher RPM with the high thrust prop.
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Specifications
Triton 2486 WABoat Type Walkaround Base Price (MSRP)$58,403.00 Length Overall25' 8''Dry Weight 4450 lbs.Beam8' 6''Fuel Cap 151 gal.Max Draft1' 6''Water Cap N/AStandard Power1x300-hp gasoline OutboardTop Cruise Speed 40 T/35 C
This is a test, right?
A question for a question.
Here is a little story about two people, we'll call them Ruth and Sumner and they live in Utah.
Well it seems that they must journey to Southern California in the winter time for some reason and being Mac sailors they bring along da boat.
Sometime during their adventure Sumner buys a dodad to calculate fuel mileage and stuff at a auto swap meet. After installing it he now has the abillity to read average and instant fuel mileage.
Sumner, after doing some expirementing, has discovered that by driving 60 mph at 2,000 rpm in 5th gear on his manual transmission he gets 18 milles per gallon on the highway. This is the sweet spot while towing the Mac.
On the way home they stop in Baker, Ca to fill up and streach their legs and all the time Sumner is saying,"how cool the new dodad is and that it really helped him find the sweet spot for towing".
Ruth says,"that nice."
Accending Baker Grade Sumner keeps the engine in the sweet spot (2,000 rpm) and notices in horor that the instant fuel mileage on the dodad is droping from 18 to 15 to 12 to 9 all the way to 6 mpg! What can be wrong, a fuel leak or some thing??
About the time they reach the summit Ruth asks," Sumner, where are your sun glasses?".
Oops, gotta turn around and go back to the gas station in Baker and get the sun glasses.
Holy Moly! Now look at the dodad, 18, 25, 50 mpg. It must be broken. We still have the boat back there and the motor is still at 2,000 rpm, no tail wind.
After retreving the sun glasses and starting back up the grade Sumner shakes his head and says, I just don't understand it,
the mileage changed from 6 to 50 mpg and I kept the rpm at 2,000 and we had the same load.
Ruth in her infinite wisdom lowers her reading glasses and says, do you think it might have something to do with the throttle position?:dance:
Did I pass
Quote:
Fuel usage and RPM really don't really equate.
A question for a question.
Here is a little story about two people, we'll call them Ruth and Sumner and they live in Utah.
Well it seems that they must journey to Southern California in the winter time for some reason and being Mac sailors they bring along da boat.
Sometime during their adventure Sumner buys a dodad to calculate fuel mileage and stuff at a auto swap meet. After installing it he now has the abillity to read average and instant fuel mileage.
Sumner, after doing some expirementing, has discovered that by driving 60 mph at 2,000 rpm in 5th gear on his manual transmission he gets 18 milles per gallon on the highway. This is the sweet spot while towing the Mac.
On the way home they stop in Baker, Ca to fill up and streach their legs and all the time Sumner is saying,"how cool the new dodad is and that it really helped him find the sweet spot for towing".
Ruth says,"that nice."
Accending Baker Grade Sumner keeps the engine in the sweet spot (2,000 rpm) and notices in horor that the instant fuel mileage on the dodad is droping from 18 to 15 to 12 to 9 all the way to 6 mpg! What can be wrong, a fuel leak or some thing??
About the time they reach the summit Ruth asks," Sumner, where are your sun glasses?".
Oops, gotta turn around and go back to the gas station in Baker and get the sun glasses.
Holy Moly! Now look at the dodad, 18, 25, 50 mpg. It must be broken. We still have the boat back there and the motor is still at 2,000 rpm, no tail wind.
After retreving the sun glasses and starting back up the grade Sumner shakes his head and says, I just don't understand it,
the mileage changed from 6 to 50 mpg and I kept the rpm at 2,000 and we had the same load.
Ruth in her infinite wisdom lowers her reading glasses and says, do you think it might have something to do with the throttle position?:dance:
Did I pass
Quote:
Fuel usage and RPM really don't really equate.
Rick why then do we use overdrive transmissions in our cars to achieve better gas mileage? Now saying that there still is an rpm that an engine is going to be most efficient at gas mileage wise. Most cars now seem to be in that range somewhere between 1800 and 2100 rpm even though their peak torque might be between 3000 and 3500.
Ok I got to get out in the shop and get something done
Sum
That is why it is an automatic and will first unlock the converter and then shift down into 3rd and maybe 2nd if it has to depending on throttle position. From what you are saying would you drive from there to here in 3rd or would you put it it 4th where it will shift into overdrive when appropriate and get much better gas mileage? This would be a not towing situation............Ruth in her infinite wisdom lowers her reading glasses and says, do you think it might have something to do with the throttle position?:dance:
Did I pass
Quote:
Fuel usage and RPM really don't really equate.
I get 20-25 mpg with my 400 HP small bock running 75-80 with the 4 speed auto and could get nowhere near that with the older 350/400 3 speed automatics. When I had a bad converter and it wouldn't lock and my rpm went up about 200-300 on the average I lost about 2 mpg right there until I put a new one in.
Of course according to GM you shouldn't even be towing in overdrive and I tow very little in overdrive with the boat, a lot with the teardrop, just some flat stretches and long down hills.
I guess you had better let them know that lower rpm's (when appropriate) won't help with fuel mileage
.By the way we will be making that drive in a month or so with our Buick that gets 30 mpg on the highway, thanks yes, to an auto with overdrive and lower rpm's!
Sum
BTW I didn't read your scenario to Ruth. I didn't really find it that amusing. Hope you got a kick out of it.
Sorry, I ment it to be funny.
I was actually trying to equate it with a small outboard motor that does not have a locking converter or a computer to read sensors and make a down shift or even fuel injection with a closed loop program.
The outboard motor just has one foward gear in the trans and one diff gear that being the prop.
If I was a betting man and had a way to check it I would bet that outboards that are carb (california air resorces board)certified or meet fed regulations are jetted to run lean around 3,000 rpm. If I could just figure a way to mount an oxygen sensor.
And we all know why there are 9.9 HP motors, right?
I was actually trying to equate it with a small outboard motor that does not have a locking converter or a computer to read sensors and make a down shift or even fuel injection with a closed loop program.
The outboard motor just has one foward gear in the trans and one diff gear that being the prop.
If I was a betting man and had a way to check it I would bet that outboards that are carb (california air resorces board)certified or meet fed regulations are jetted to run lean around 3,000 rpm. If I could just figure a way to mount an oxygen sensor.
And we all know why there are 9.9 HP motors, right?
My apologies for beating and then dragging, possibly kicking and then dragging again a dead horse... But I was of course thinking about the dreaded "prop slip" again over the weekend in regards to a displacement hull and here is another slightly different way of looking at things (no reference, Im making this all up, could be wrong).
One assumption I'm making here is that a 10 pitch prop doing one revolution pushes the same amount of water as a 5 pitch prop doing two revolutions. In either case, I have pushed a volume of water 10 inches long. This also says that the thrust of a 10 pitch prop at a given RPM is the same as the thrust of a 5 pitch prop at TWICE the RPM. Assuming this is true...
First, we run the boat for one minute and find the distance traveled (ie, constant speed). We did the test with a 10 pitch prop and can calculate the prop slip ratio based on the distance traveled and the calculated prop travel.
Next, we put on a 5 pitch prop. We run the boat at the same exact speed as last time so cover the same distance and this requires the same amount of thrust as last time since the speeds are identical. From our original assumption, the same thrust required the 5 pitch prop to run at twice the RPM as the 10 pitch prop.
Note that the "distance traveled calculation" for the 10 pitch prop at one RPM is identical to the 5 pitch prop at twice the RPM.
So the calculated prop slip is the exactly same number for either the 5 pitch or the 10 pitch prop - at the test boat speed. Ie, prop slip is not dependent on prop pitch (if you believe the original assumption). It relates more to the efficiency of the hull - see below:
Another sort of interesting experiment.
If a displacement hull is going 2 mph, there is very little drag and regardless of what pitch prop is used, the prop hardly needs to work and therefore, the prop distance will be about the same as the boat distance and a very low prop slip number will result.
Now the same displacement hull is run at 6 mph. Friction drag has increased and you are also getting near hull speed. So now because of the higher resistance of the hull, the prop must work harder - push more water and the distance the prop has traveled (regardless of pitch) will be a fair amount larger than the distance the boat traveled. When prop slip is calculated, now it is a significant higher number - like maybe 20%.
Now the hull is run as hard as the outboard will allow - ie, wide open throttle. In this case, the hull is up against hull speed and the outboard is pushing out a lot of water but the hull is not going any faster. The prop slip number now is a very high number - lets say 50% as the prop travel was a lot higher than actual boat travel. Not very efficient - and we also get a high prop slip number. But in this case, the pitch does make a difference because the low pitch prop allows the outboard to run at a better power band so it can push out more water than the high pitch prop. So the low pitch prop can produce an even higher (worse) prop slip number than the high pitch prop and get a tiny bit more speed - but we don't really care since no one operates a boat like this, its not efficient at all (ok, maybe once in a while.. just to see).
So we see that the prop slip number more closely follows hull drag. For a displacement hull, it will be a very low number at low speeds. It will gradually increase with boat speed and then starts to rise dramatically as the displacement hull speed limit is reached..
Timebandit, one lake I know in Colorado has a rule that boat motors must be less than 10 hp.
One assumption I'm making here is that a 10 pitch prop doing one revolution pushes the same amount of water as a 5 pitch prop doing two revolutions. In either case, I have pushed a volume of water 10 inches long. This also says that the thrust of a 10 pitch prop at a given RPM is the same as the thrust of a 5 pitch prop at TWICE the RPM. Assuming this is true...
First, we run the boat for one minute and find the distance traveled (ie, constant speed). We did the test with a 10 pitch prop and can calculate the prop slip ratio based on the distance traveled and the calculated prop travel.
Next, we put on a 5 pitch prop. We run the boat at the same exact speed as last time so cover the same distance and this requires the same amount of thrust as last time since the speeds are identical. From our original assumption, the same thrust required the 5 pitch prop to run at twice the RPM as the 10 pitch prop.
Note that the "distance traveled calculation" for the 10 pitch prop at one RPM is identical to the 5 pitch prop at twice the RPM.
So the calculated prop slip is the exactly same number for either the 5 pitch or the 10 pitch prop - at the test boat speed. Ie, prop slip is not dependent on prop pitch (if you believe the original assumption). It relates more to the efficiency of the hull - see below:
Another sort of interesting experiment.
If a displacement hull is going 2 mph, there is very little drag and regardless of what pitch prop is used, the prop hardly needs to work and therefore, the prop distance will be about the same as the boat distance and a very low prop slip number will result.
Now the same displacement hull is run at 6 mph. Friction drag has increased and you are also getting near hull speed. So now because of the higher resistance of the hull, the prop must work harder - push more water and the distance the prop has traveled (regardless of pitch) will be a fair amount larger than the distance the boat traveled. When prop slip is calculated, now it is a significant higher number - like maybe 20%.
Now the hull is run as hard as the outboard will allow - ie, wide open throttle. In this case, the hull is up against hull speed and the outboard is pushing out a lot of water but the hull is not going any faster. The prop slip number now is a very high number - lets say 50% as the prop travel was a lot higher than actual boat travel. Not very efficient - and we also get a high prop slip number. But in this case, the pitch does make a difference because the low pitch prop allows the outboard to run at a better power band so it can push out more water than the high pitch prop. So the low pitch prop can produce an even higher (worse) prop slip number than the high pitch prop and get a tiny bit more speed - but we don't really care since no one operates a boat like this, its not efficient at all (ok, maybe once in a while.. just to see).
So we see that the prop slip number more closely follows hull drag. For a displacement hull, it will be a very low number at low speeds. It will gradually increase with boat speed and then starts to rise dramatically as the displacement hull speed limit is reached..
Timebandit, one lake I know in Colorado has a rule that boat motors must be less than 10 hp.
Possibly for the Mac M and X boats..
After going through this prop slip stuff.. I finally see how the power boat pitch calculator works. Its doesn't really apply to a displacement hull but it would apply to an X or M and here is an example.
Lets say you have a 4500 pound boat with a Nissan 70 HP, gear ratio 2.3 to 1, Max HP-RPM is 5500 RPM. Prop pitch range from 11 to 21.
If you first go to this website http://www.go-fast.com/boat_speed_predictions.htm
You get two pieces of information. First lets assume that a M hull is closer to the heavy V bottom and therefore will have a similar prop slip when planing - lets assume its 13%.
On this same page, plug in weight = 4500, HP=70 and you get a calculated speed of 28 (assume mph, doesn't matter since we will just plug the same number into the next calculator)..
Next, we go to the prop slip calculator here http://www.go-fast.com/Prop_Slip_Calculator.htm
In the prop slip calculator, we plug in gear ratio = 2.3, RPM=5500, slip = 13% and actual speed = 28
Then push the "Calc T" button and it calculates a theoretical speed of 32.
Then push Pitch calculate and it shows a pitch of 14.
I don't know if this matches reality for a X or M model or not and it based on picking a prop slip number of 13%.
Note also that someone who has an M or an X and has already found the optimum prop could also use the calculator to find approximately what the prop slip number is for these boats. I assumed 13%, maybe its off?? Might even be that the X hull has a slightly lower prop slip number than the M hull since I understand its a little better power boat.
Once again, these calculators are for power boats trying to achieve a peak speed by allowing the motor to acheive its peak power band RPM. They know from previous experience about what the prop slip is for a hull going at its fastest. The calculator then finds the correct prop pitch so that it puts the outboard RPM at its best power band for the expected top speed to be achieved.
Not something which concerns me much since I have a displacement hull.. but interesting.
After going through this prop slip stuff.. I finally see how the power boat pitch calculator works. Its doesn't really apply to a displacement hull but it would apply to an X or M and here is an example.
Lets say you have a 4500 pound boat with a Nissan 70 HP, gear ratio 2.3 to 1, Max HP-RPM is 5500 RPM. Prop pitch range from 11 to 21.
If you first go to this website http://www.go-fast.com/boat_speed_predictions.htm
You get two pieces of information. First lets assume that a M hull is closer to the heavy V bottom and therefore will have a similar prop slip when planing - lets assume its 13%.
On this same page, plug in weight = 4500, HP=70 and you get a calculated speed of 28 (assume mph, doesn't matter since we will just plug the same number into the next calculator)..
Next, we go to the prop slip calculator here http://www.go-fast.com/Prop_Slip_Calculator.htm
In the prop slip calculator, we plug in gear ratio = 2.3, RPM=5500, slip = 13% and actual speed = 28
Then push the "Calc T" button and it calculates a theoretical speed of 32.
Then push Pitch calculate and it shows a pitch of 14.
I don't know if this matches reality for a X or M model or not and it based on picking a prop slip number of 13%.
Note also that someone who has an M or an X and has already found the optimum prop could also use the calculator to find approximately what the prop slip number is for these boats. I assumed 13%, maybe its off?? Might even be that the X hull has a slightly lower prop slip number than the M hull since I understand its a little better power boat.
Once again, these calculators are for power boats trying to achieve a peak speed by allowing the motor to acheive its peak power band RPM. They know from previous experience about what the prop slip is for a hull going at its fastest. The calculator then finds the correct prop pitch so that it puts the outboard RPM at its best power band for the expected top speed to be achieved.
Not something which concerns me much since I have a displacement hull.. but interesting.
This is for those that may not understand max hull speed of a positive displacement boat and why more horse power won't make it go faster.
http://www.solarnavigator.net/wave_drag_boat_design.htm
http://www.solarnavigator.net/wave_drag_boat_design.htm
One final thing on this project.. Ive got two big 6 volt golf cart batteries in series storing a huge amount of energy and four gauge wires running the length of the boat.. so figured I needed maybe a couple more safety things on the DC power side.
First, not sure of the benefits of a breaker over a fuse - but I changed to a 90 amp breaker. I partly did this because it mounts where I can easily get to it in case it trips or I need to shut things down (the previous fuse was inside the Vberth storage - could have been hard to get to if that area was full of water jugs for example) . The breaker is also a switch and before, I had no way to completely disconnect the batteries - now I do with the breaker/switch. The breaker/switch is mounted in the head area and its backside opens to the Vberth storage where the batteries are.
I thought it was probably a good idea to be able to independently disconnect the outboard DC from the rest of the 12 volt system. Also, I wanted to be able to easily turn the power off to the breakout box in the Laz when I'm connecting up the outboard DC power lines. I ended up putting in a battery switch next to the the breakout box. This seems like an OK place since the switch wont accidentally get turned off when the outboard is running by some kid messing with things. The switch is also before the capacitor in the breakout box and I'm about 98% sure that this will protect the rectifier in the outboard charging system regardless..
Also attached is the updated wiring diagram..
First, not sure of the benefits of a breaker over a fuse - but I changed to a 90 amp breaker. I partly did this because it mounts where I can easily get to it in case it trips or I need to shut things down (the previous fuse was inside the Vberth storage - could have been hard to get to if that area was full of water jugs for example) . The breaker is also a switch and before, I had no way to completely disconnect the batteries - now I do with the breaker/switch. The breaker/switch is mounted in the head area and its backside opens to the Vberth storage where the batteries are.
I thought it was probably a good idea to be able to independently disconnect the outboard DC from the rest of the 12 volt system. Also, I wanted to be able to easily turn the power off to the breakout box in the Laz when I'm connecting up the outboard DC power lines. I ended up putting in a battery switch next to the the breakout box. This seems like an OK place since the switch wont accidentally get turned off when the outboard is running by some kid messing with things. The switch is also before the capacitor in the breakout box and I'm about 98% sure that this will protect the rectifier in the outboard charging system regardless..
Also attached is the updated wiring diagram..
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Looks nice Walt. Who's breaker did you use?
An electrical contractor here said that some AC breakers were rated for DC and some weren't. I don't know if that is true on not. He told me that a Square D was rated for DC, so that is what I got. Just thought I would pass that on.
Where did you get the capacitor? Do you have a number on it? That might be a good idea and something I'd like to to also. I"ll have my outboard wired to the batteries all the time, but like you if the breaker would trip or for some reason I'd throw it (in picture above) the OB would no longer be connected.
c ya,
Sum
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An electrical contractor here said that some AC breakers were rated for DC and some weren't. I don't know if that is true on not. He told me that a Square D was rated for DC, so that is what I got. Just thought I would pass that on.
Where did you get the capacitor? Do you have a number on it? That might be a good idea and something I'd like to to also. I"ll have my outboard wired to the batteries all the time, but like you if the breaker would trip or for some reason I'd throw it (in picture above) the OB would no longer be connected.
c ya,
Sum
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This is the breaker switch I used http://www.jamestowndistributors.co...a+Systems+187+Series+Thermal+Circuit+Breakers
It comes in all sorts of currents. I picked 90 amp, 100 amp or even 130 amp might have been a little better choice. Some breakers don't like the switch being used a lot. I'm not sure about this one but the switch wont get used much anyhow. Ive used the home breaker for DC in the past.. seemed to work fine.
Regarding the capacitor, this is probably something you already know but its purpose is to keep the charged coil in the alternator from generating a big voltage spike if it gets disconnected from the battery while its running. The big voltage spike can be high enough to reverse breakdown the rectifier diodes and it doesn't take much current to blow them up at the high voltage.
Xantrex makes something called a Zap Stop http://www.xantrex.com/web/id/239/p/1/pt/7/product.asp which does the same thing as the cap - only it clamps the voltage and absorbs the discharge - rather than prevent the high voltage like the cap does.
I have shown a 220 uf 100 volt cap in the diagram and I picked the voltage based on looking at the Honda output on a Oscilloscope and I don't remember exact numbers but I seem to remember 40 to 50 volts on the output when there is no load. Since I may want to use the outboard sometimes with it disconnected from the battery (no regulation of the current - if the batteries are already completely full, I don't want the outboard trying to jam more current in) so I picked 100 volt.
You probably could get by with about 1/2 the capacitance - like 100 uf but it doesn't hurt to go with 220 uf and I'm fairly sure it will protect the outboard rectifier. My "capacitor" is made from whatever I had around and is actually composed of a bunch of smaller caps. But a fairly simple solution might be something like this:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=P10327-ND
Its a 390 uf 50 volt cap. Since you need 100 volts, you need to put two of them in series. But when you series caps, you end up with 1/2 the capacitance. So two of these in series would be 195 uf 100 volt. I got some caps out of old home stereos, others I had laying around and you can put them in various combination of Parallel and series to get the final cap you need. Putting two caps in parallel doubles the cap value. Two in series gives 1/2 the cap value but twice the voltage. These type of caps are polarity sensitive and go off like a fire cracker if you hook them up backwards.
It comes in all sorts of currents. I picked 90 amp, 100 amp or even 130 amp might have been a little better choice. Some breakers don't like the switch being used a lot. I'm not sure about this one but the switch wont get used much anyhow. Ive used the home breaker for DC in the past.. seemed to work fine.
Regarding the capacitor, this is probably something you already know but its purpose is to keep the charged coil in the alternator from generating a big voltage spike if it gets disconnected from the battery while its running. The big voltage spike can be high enough to reverse breakdown the rectifier diodes and it doesn't take much current to blow them up at the high voltage.
Xantrex makes something called a Zap Stop http://www.xantrex.com/web/id/239/p/1/pt/7/product.asp which does the same thing as the cap - only it clamps the voltage and absorbs the discharge - rather than prevent the high voltage like the cap does.
I have shown a 220 uf 100 volt cap in the diagram and I picked the voltage based on looking at the Honda output on a Oscilloscope and I don't remember exact numbers but I seem to remember 40 to 50 volts on the output when there is no load. Since I may want to use the outboard sometimes with it disconnected from the battery (no regulation of the current - if the batteries are already completely full, I don't want the outboard trying to jam more current in) so I picked 100 volt.
You probably could get by with about 1/2 the capacitance - like 100 uf but it doesn't hurt to go with 220 uf and I'm fairly sure it will protect the outboard rectifier. My "capacitor" is made from whatever I had around and is actually composed of a bunch of smaller caps. But a fairly simple solution might be something like this:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=P10327-ND
Its a 390 uf 50 volt cap. Since you need 100 volts, you need to put two of them in series. But when you series caps, you end up with 1/2 the capacitance. So two of these in series would be 195 uf 100 volt. I got some caps out of old home stereos, others I had laying around and you can put them in various combination of Parallel and series to get the final cap you need. Putting two caps in parallel doubles the cap value. Two in series gives 1/2 the cap value but twice the voltage. These type of caps are polarity sensitive and go off like a fire cracker if you hook them up backwards.
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