There has been a previous discussion about this and it was indicated that a Solas four blade prop was available. Re-reading the thread it appears the Solas 4 blade was for a BF15 not 5HP. The 5 has a pindrive hub and I cannot find any information on web about a replacement prop to help stop my boat or be effective in reverse. Any thoughts would be appreciated.
Honda BF5a 5 HP - High Thrust Prop
- Thread starter PaulE
- Start date
My Mac came with an 8 HP Honda and I wanted a higher thrust prop but could never find one. Your 5 HP might even take the same prop, don't know. Anyway I found the place in this link.....
http://www.midwestpropeller.com/
... and was able to buy a prop from them that they also changed the pitch on all for about $100. Not sure what they charge now but maybe call them. Nice folks to deal with and I was real happy with the prop. It looked like a factory prop after they did the re-pitch, very professional job and prompt service,
Sumner
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Look all the way near the bottom of the list for original equipment
http://marine.honda.com/parts/accessories/categories/propellers
I believe the lower pitch is the high thrust prop
58130-ZV1-941ZB
http://marine.honda.com/parts/accessories/categories/propellers
I believe the lower pitch is the high thrust prop
58130-ZV1-941ZB
If you can get a metal prop for the 5HP I think they can re-pitch it,
Sumner
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A suggestion..
If the current prop doesn’t do well in reverse, just re-pitching it probably won’t help.
5 hp on a 22 foot boat is likely already getting the boat up against the theoretical hull speed wall. Re-pitching (probably to a lower pitch) will allow the prop to spin faster and get a little more hp - but you wont go any faster since you were already getting to hull speed. You will however make the outboard louder, use more gas and vibrate more because it will now need to run at higher rpm for the same speed.
If the prop was poor before in reverse, it will still be poor after it’s repitched.
For good reverse, you need a prop with a wide hub so that the exhaust doesn’t flow over the blades in reverse (assuming you have through the hub exhaust). Props that are good in reverse also tend to have symmetrical blade shapes so the blade works the same regardless of which direction they are turning. Things that make the prop work well in reverse have a tradeoff, the prop is probably not as efficient as one optimized for mainly forward.
If you do just repitch, this would be very interesting to everyone..
With the old prop, use a gps to measure your boats speed at full throttle. Then at full speed, put the outboard in reverse and measure how long it takes you to stop.
Do the same with the new prop.. If you get a prop that is good in reverse, you will measure a big difference in how long it takes to stop. If you just re-pitch, I would bet you can hardly measure any diffference before and after.
Walt makes some good points. Most "high thrust" props have elephant ear blades to push more water, and are also larger diameter. This would certainly help with reversing, as it can throw more water. I had never thought that the elephant ear blades being symmetrically shaped would equate to more equivalent thrust forward and in reverse, but that makes sense to me.
Also, think of the prop as a wood screw trying to get through water. As the prop spins, it wants to move forward it's given length (based on the pitch.) This equates to a given speed at given RPM. Now, if you take that prop which wants to go fast (move forward more per rev,) because it's got a bigger pitch for a planing hull, and you prevent it moving it's distance and speed because it's on a displacement hull, it will have far more slip and be less efficient. And will probably prevent the motor turning fast enough to get into proper RPM territory.
Also, think of the prop as a wood screw trying to get through water. As the prop spins, it wants to move forward it's given length (based on the pitch.) This equates to a given speed at given RPM. Now, if you take that prop which wants to go fast (move forward more per rev,) because it's got a bigger pitch for a planing hull, and you prevent it moving it's distance and speed because it's on a displacement hull, it will have far more slip and be less efficient. And will probably prevent the motor turning fast enough to get into proper RPM territory.
Just an opinion.. but I think the larger hub that allows the exhaust to exit through the hub rather than over the prop blades may be what makes the main difference in reverse..
When you talk about "slip", a prop must have slip in order to generate thrust. No slip means the prop would be just turning at the same speed as the water - no thrust. Its thrust that matters, and F = ma. You can get more F by either increasing m (pushing more water) or by increasing a (pushing the water faster).. I think that’s were diameter and blade area come into play.
If you have an outboard that has excess hp (like a 5 hp on a 22 foot boat), a "wrong" prop that typically comes with the outboard won’t allow the outboard to spin up its rpm where max hp is delivered.. but it does generate enough hp to get up to hull speed. Re-pitch to a lower pitch allows the outboard to run at a higher rpm and achieve a little higher hp - and thrust.. but since you were already at hull speed it doesn’t buy anything.
If you had an outboard that wasn’t getting you up to hull speed because it was operating at too low of rpm and wasn’t generating enough thrust, then you would benefit by lowering the pitch of the prop..
Another example of why "slip" has more to do with hull effiency. Say we take an outboard/prop and put it on one boat that is 15 foot long and weighs 10 thousand pounds (ie, real heavy not efficient hull). Then we take the same outboard/prop and put it on another hull that is 30 foot long and wieghs 500 pounds (ie, a very efficent light hull).
To make both hulls go the same exact speed, the outboard has to generate a lot more thrust with the heavier boat. To generate more thrust, the prop must turn faster and since the speed in the water was exactly the same the prop on the heavy boat had to operate at a lot higher "slip". The prop efficiency didnt change between the two cases but the hulll efficiency did and that is what resulted in the change in prop slip..
When you talk about "slip", a prop must have slip in order to generate thrust. No slip means the prop would be just turning at the same speed as the water - no thrust. Its thrust that matters, and F = ma. You can get more F by either increasing m (pushing more water) or by increasing a (pushing the water faster).. I think that’s were diameter and blade area come into play.
If you have an outboard that has excess hp (like a 5 hp on a 22 foot boat), a "wrong" prop that typically comes with the outboard won’t allow the outboard to spin up its rpm where max hp is delivered.. but it does generate enough hp to get up to hull speed. Re-pitch to a lower pitch allows the outboard to run at a higher rpm and achieve a little higher hp - and thrust.. but since you were already at hull speed it doesn’t buy anything.
If you had an outboard that wasn’t getting you up to hull speed because it was operating at too low of rpm and wasn’t generating enough thrust, then you would benefit by lowering the pitch of the prop..
FYI, I dont think the amount of slip has much to do with prop efficiency (but it does have something to do with hull efficiency). For example, if you have an outboard at half throttle and you are getting to hull speed, you will have some slip from that prop - easy to see since you are pushing a bunch of water out the back. Now increase the thrust to full throttle. More water will be pushed out the back because of more slip (that is how you get thrust - no slip = no thrust). The prop wasnt less efficient. You just dont go any faster because your already at hull speed.
Another example of why "slip" has more to do with hull effiency. Say we take an outboard/prop and put it on one boat that is 15 foot long and weighs 10 thousand pounds (ie, real heavy not efficient hull). Then we take the same outboard/prop and put it on another hull that is 30 foot long and wieghs 500 pounds (ie, a very efficent light hull).
To make both hulls go the same exact speed, the outboard has to generate a lot more thrust with the heavier boat. To generate more thrust, the prop must turn faster and since the speed in the water was exactly the same the prop on the heavy boat had to operate at a lot higher "slip". The prop efficiency didnt change between the two cases but the hulll efficiency did and that is what resulted in the change in prop slip..
When you say you are looking for a prop to help you stop the boat what comes into my mind is an attempt to make a sailboat handle like a powerboat. In my experience I have found that the best way to operate a sailboat with an outboard in reverse is with finesse and not power. Gauge the effects of wind and current and backup the boat in idle or as slow as an engine speed that you can maintain for some steerage. Use the engine just to maintain motion and make small corrections in conjunction with the rudder .
I think there is one case where a very good reverse matters and that is if you can’t vector the outboard thrust and you have a boat with high aspect foils. The problem with the high aspect foils is that they tend to stall at very low speeds. So if your coming into a slip and you can’t vector the outboard, you need to go a little faster to keep the underwater foils working and in control. Then.. the very good reverse becomes valuable as you can stop very fast.
I had a high thrust/ great reverse prop for a while.. just didn’t like it because of the higher rpm needed - and resulting higher noise and vibration. I went back to a conventional prop and like it MUCH better. However, I can vector the outboard so can come in to slip at fairly low speeds and the instant stop isn’t so important. I have always felt the conventional prop was more than adequate for stoping and a lot nicer if you motor (forward) for any distance at all.
I did measure the time it takes my conventional "swept back blade higher pitch optimized for forward only" prop to stop my boat (a 1990 Mac 26S with a 9.8 hp outboard). I got the boat up to full speed - around 7 knts - and it took 10 seconds to come to a full stop.
I had a high thrust/ great reverse prop for a while.. just didn’t like it because of the higher rpm needed - and resulting higher noise and vibration. I went back to a conventional prop and like it MUCH better. However, I can vector the outboard so can come in to slip at fairly low speeds and the instant stop isn’t so important. I have always felt the conventional prop was more than adequate for stoping and a lot nicer if you motor (forward) for any distance at all.
I did measure the time it takes my conventional "swept back blade higher pitch optimized for forward only" prop to stop my boat (a 1990 Mac 26S with a 9.8 hp outboard). I got the boat up to full speed - around 7 knts - and it took 10 seconds to come to a full stop.
Thanks for all who commented, Sumner, Tom, Walt, Brian & Benny. Plenty of food for thought there. I am going to do more testing on Lake Taupo first - it may be more to do with the rake of the outboard and the movement of motor when thrown into reverse inside motor well. I am going to try to improve the engine mounting system inside well; will report back in due course. Having a great summer here folks. Best, Paul