I have a 30ft boat with a 5411, 11hp motor with a 2 blade prop. It is very under powered. Has anybody ever changed out there 2 blade for a 3 blade prop? Would this be too much for the motor? Transmission? I don't race so the added drag wouldn't bother me too much. If it's OK,....what size, pitch, etc. Thanks
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Bob, 3 blades is more efficient and could
help a little but mostly you are underpowered. Underpowering auxiliary sailboat engines is common because if you use more power than you need to reach hull speed it just gets wasted.
help a little but mostly you are underpowered. Underpowering auxiliary sailboat engines is common because if you use more power than you need to reach hull speed it just gets wasted.
Bob, you need to be a little more diffinitive
Bietzpadlin is a 30 foot Islander with a 10 HP volvo a 3:1 reduction gear and a 13x15 three blade prop. I am told that I could swing a 15x10 three blade if I had the room. I can get 5.5 knots in flat water and have plenty of thrust for docking and breaking out a well dug in anchor. I did have a 13x7 two blade sailorman prop that would allow me to run 3200 rpm with the boat tied to the dock. You can't waste power with a diesel, you simply don't use it.
Bietzpadlin is a 30 foot Islander with a 10 HP volvo a 3:1 reduction gear and a 13x15 three blade prop. I am told that I could swing a 15x10 three blade if I had the room. I can get 5.5 knots in flat water and have plenty of thrust for docking and breaking out a well dug in anchor. I did have a 13x7 two blade sailorman prop that would allow me to run 3200 rpm with the boat tied to the dock. You can't waste power with a diesel, you simply don't use it.
Which problem are you having...
Bob, I went from a 2 blade to a 3 blade to get more usable power out of my 8 hp Yanmar. You need to tell us if your problem is too much prop or not enough. You must be having one of two problems: 1) Diesel at max rpm but not enough power, or 2) Diesel can't get up to max rpm. Which is yours?
Bob, I went from a 2 blade to a 3 blade to get more usable power out of my 8 hp Yanmar. You need to tell us if your problem is too much prop or not enough. You must be having one of two problems: 1) Diesel at max rpm but not enough power, or 2) Diesel can't get up to max rpm. Which is yours?
Not enough speed
I only get about 4.5 knots in flat water. There's no problem with the motor she run fine. We were out on Christmas Eve and was motoring into the wind and against the tide the last couple of miles because it was getting late and it was all I could do to get 2.5 to 3 knots out of her. I need more speed. Thanks
I only get about 4.5 knots in flat water. There's no problem with the motor she run fine. We were out on Christmas Eve and was motoring into the wind and against the tide the last couple of miles because it was getting late and it was all I could do to get 2.5 to 3 knots out of her. I need more speed. Thanks
Bob, where are you on The Bay?
There are places where the current runs well over 1.5 knots. When you put the engine in gear does it load up or show a small drop in RPM? If not, then your prop isn't absorbing enough power. Tell us your diameter and pitch on this 2 blade prop? When you advance the throttle to wide open, do you quickly get full engine speed?
There are places where the current runs well over 1.5 knots. When you put the engine in gear does it load up or show a small drop in RPM? If not, then your prop isn't absorbing enough power. Tell us your diameter and pitch on this 2 blade prop? When you advance the throttle to wide open, do you quickly get full engine speed?
Prop
We are near Little creek. We were also at the mouth of the bay coming through the bridge opening against the current and we could only get 1.5 knots. The motor runs great. Never slows down or bogs down. Gets up the RPM's in a hurry but takes a little time to get the boat up to speed. I'm told that this boat with this motor is under powered. As far as the size of the prop and pitch I don't know what it is. We bought this boat in May and feel it's the one that came with the boat. We love the boat (Catalina 30 1980)just need more power.
We are near Little creek. We were also at the mouth of the bay coming through the bridge opening against the current and we could only get 1.5 knots. The motor runs great. Never slows down or bogs down. Gets up the RPM's in a hurry but takes a little time to get the boat up to speed. I'm told that this boat with this motor is under powered. As far as the size of the prop and pitch I don't know what it is. We bought this boat in May and feel it's the one that came with the boat. We love the boat (Catalina 30 1980)just need more power.
Bob, I went to Boatdiesel for their calculator and
got these results: Allowing for 9500 pounds of boat, 26 feet waterline, 2:1 transmission ratio, 3200 top RPM, 5.7 knots top speed, 2600 cruising RPM, 4.4 knots. Propellor should be 12 inch diameter 7 inch pitch, 3 blades. That combination will absorb 10.7 HP at 3200 RPM and 4.5 HP at 2600 RPM.
got these results: Allowing for 9500 pounds of boat, 26 feet waterline, 2:1 transmission ratio, 3200 top RPM, 5.7 knots top speed, 2600 cruising RPM, 4.4 knots. Propellor should be 12 inch diameter 7 inch pitch, 3 blades. That combination will absorb 10.7 HP at 3200 RPM and 4.5 HP at 2600 RPM.
Sadly, your problem is not enough engine..
11 hp won't push a 30ft sailboat fast enough regardless of what prop you have on it. I think that a 3 blade prop will only load up the engine more and slow you down further. You could try a very small 3 blade prop or adjust the pitch on your 2 blade for more bite. Good luck.
11 hp won't push a 30ft sailboat fast enough regardless of what prop you have on it. I think that a 3 blade prop will only load up the engine more and slow you down further. You could try a very small 3 blade prop or adjust the pitch on your 2 blade for more bite. Good luck.
Bob, following the lead of Landsend I
went back to Boatdiesel's calculator and ran the same boat numbers with a 35 hp engine and got the following Top speed at 3200 rpm 8.3 knots at 34 hp and 2 gallons per hour. Crusing at 2600 17 hp at 6.6 knots and 1 gallon per hour. Hull speed 6.8 at 19 hp. Propeller size:15.4x10 three blades . Now you have the choice to make and the cost in fuel for the extra speed.
went back to Boatdiesel's calculator and ran the same boat numbers with a 35 hp engine and got the following Top speed at 3200 rpm 8.3 knots at 34 hp and 2 gallons per hour. Crusing at 2600 17 hp at 6.6 knots and 1 gallon per hour. Hull speed 6.8 at 19 hp. Propeller size:15.4x10 three blades . Now you have the choice to make and the cost in fuel for the extra speed.
Prop won't..
The 3 blade prop won't make much difference in flat water but it will get more bite with a head wind and some chop. A properly sized three blade won't load your engine any more than a properly sized two blade but it will be much less likely to cavitate. The first thing I would check is the accuracy of your tachometer. A good number of boat tachs are off by quite a bit. Perhaps what you consider a cruising RPM is not a cruising RPM and is low because your tach is off. Once you know your tach is correct make sure you can run your engine, under load, to max RPM. If you can't get to max RPM you could be over pitched or over propped which would cause poor performance. Yes a 5411 is a small engine but it should push your boat at more than 2-3 knots... To check your tach it's a good idea to own a Digital Laser Photo Tachometer. I use mine for lots of things such as making sure my pulley sizez on my alternator are the proper size and it's spinning at it's most efficient speed and to check on my tachometer. The $89.00 will pay for itself in the first use if you find something is off.... Digital Laser Photo Tachometer: http://www.eastwoodco.com/jump.jsp?itemID=16368&itemType=PRODUCT
The 3 blade prop won't make much difference in flat water but it will get more bite with a head wind and some chop. A properly sized three blade won't load your engine any more than a properly sized two blade but it will be much less likely to cavitate. The first thing I would check is the accuracy of your tachometer. A good number of boat tachs are off by quite a bit. Perhaps what you consider a cruising RPM is not a cruising RPM and is low because your tach is off. Once you know your tach is correct make sure you can run your engine, under load, to max RPM. If you can't get to max RPM you could be over pitched or over propped which would cause poor performance. Yes a 5411 is a small engine but it should push your boat at more than 2-3 knots... To check your tach it's a good idea to own a Digital Laser Photo Tachometer. I use mine for lots of things such as making sure my pulley sizez on my alternator are the proper size and it's spinning at it's most efficient speed and to check on my tachometer. The $89.00 will pay for itself in the first use if you find something is off.... Digital Laser Photo Tachometer: http://www.eastwoodco.com/jump.jsp?itemID=16368&itemType=PRODUCT
Way underpowered
It was several years ago that I read an article on the history of Catalina 30's. My mind isnt so sharp anymore, so I may be a little off, but from what I recall, at one time, the engines on the 30's were optional. Sometime in the early 1980's, Catalina realized that the optional smaller engines were a big mistake. They then standardized the engines and I cant remember the HP, but I think it was a 23HP engine. The smaller engines were so inadequate that it is evidenced in the great disparity in price in the low HP engines. The 10 -13 HP ranges were only good for sheltered lakes. The 18HP is marginal in performance in the Gulf of Mexico where you will have headwinds and waves. It doesnt take much of a wavelet to stop an 18HP in its tracks. The 23HP to 25HP seem to be just about right for most coastal conditions. IMHO Former Cat 30 owner. BTW....great boat overall. I love Catalinas Tony B
It was several years ago that I read an article on the history of Catalina 30's. My mind isnt so sharp anymore, so I may be a little off, but from what I recall, at one time, the engines on the 30's were optional. Sometime in the early 1980's, Catalina realized that the optional smaller engines were a big mistake. They then standardized the engines and I cant remember the HP, but I think it was a 23HP engine. The smaller engines were so inadequate that it is evidenced in the great disparity in price in the low HP engines. The 10 -13 HP ranges were only good for sheltered lakes. The 18HP is marginal in performance in the Gulf of Mexico where you will have headwinds and waves. It doesnt take much of a wavelet to stop an 18HP in its tracks. The 23HP to 25HP seem to be just about right for most coastal conditions. IMHO Former Cat 30 owner. BTW....great boat overall. I love Catalinas Tony B
Changing the criteria from 3 blades to 2 blades
changed the prop diameter for the last example to 16.4 inches and the pitch to 9.9 inches. In the first example the change is to a 13x7.5 propellor. But in each case they recommend a lower gear ratio and larger prop for better propellor efficiency.
changed the prop diameter for the last example to 16.4 inches and the pitch to 9.9 inches. In the first example the change is to a 13x7.5 propellor. But in each case they recommend a lower gear ratio and larger prop for better propellor efficiency.
This discussion seems to be a debate about
what constitutes adequate boat speed. I know that when we are ready to go home we can get in a hurry but sailing at 4-5 knots is quite pleasant and that is about all you can get from 10 knots apparent. Yet at 10 knots wind we can go to the weather in a fair chop and not be stopped. I run 10 hp and in heavy seas I throttle back a bit when heading into the waves. I have gone to the weather in 25 knots and would not have wanted more speed.
what constitutes adequate boat speed. I know that when we are ready to go home we can get in a hurry but sailing at 4-5 knots is quite pleasant and that is about all you can get from 10 knots apparent. Yet at 10 knots wind we can go to the weather in a fair chop and not be stopped. I run 10 hp and in heavy seas I throttle back a bit when heading into the waves. I have gone to the weather in 25 knots and would not have wanted more speed.
I've always wondered
how does one find the right mix of gear ratio vs pitch? Is there a preference for slower-turning props with a lot of pitch vs a faster-spinning prop with less pitch? I know a lot of us are stuck with a gear ratio and thus only change pitch, but if you could change either, would you want a new gear ratio?
how does one find the right mix of gear ratio vs pitch? Is there a preference for slower-turning props with a lot of pitch vs a faster-spinning prop with less pitch? I know a lot of us are stuck with a gear ratio and thus only change pitch, but if you could change either, would you want a new gear ratio?
Brian M H 23, I spent one winter studying
The Propeller Book by Dave Gear. And then I made my choice because I was buying new drive train. I also consulted with Vosbury Marine the Volvo dealer that sold me the engine. a couple of years ago I found "Boatdiesel.com" and that is where I go for quick answers for discussions here.
The Propeller Book by Dave Gear. And then I made my choice because I was buying new drive train. I also consulted with Vosbury Marine the Volvo dealer that sold me the engine. a couple of years ago I found "Boatdiesel.com" and that is where I go for quick answers for discussions here.
Clean Prop???
I had a few barnacles on my prop and couldn't do four knots!!!! I feel foolish for asking such an obvious question but is the prop clean???
I had a few barnacles on my prop and couldn't do four knots!!!! I feel foolish for asking such an obvious question but is the prop clean???
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