My 1964 Allied seabreeze ( 35' , 14000 lbs, full keel ) was repowered by the P.O with a Yanmar 20QM and my broker suggested that the prop may not be ideal for the new set up. Does anyone could suggest a proper size /pitch for this engine on a full keel heavy displacement boat ?
Which prop ?
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KoolFrog—
When asking a question like this, it would help to say what the gear ratio of the transmission is, as well as what the WOT RPM of the engine is, as well as the diameter of the prop aperture, if any, is. These are all crucial in figuring out what prop might work. Hopefully, someone has an Allied Seabreeze 35 with the same engine and transmission and can say what prop as worked for them.
Your best bet is to talk to a propellor shop and get them to help you come up with the right prop for you boat. Sizing a prop is more an art than a science, since there are a lot more variables than just transmission gear ratio, engine HP, boat displacement and prop size and pitch that go into it. Dave Gerr's The Propellor Handbook is an excellent book for you to read on this subject.
When asking a question like this, it would help to say what the gear ratio of the transmission is, as well as what the WOT RPM of the engine is, as well as the diameter of the prop aperture, if any, is. These are all crucial in figuring out what prop might work. Hopefully, someone has an Allied Seabreeze 35 with the same engine and transmission and can say what prop as worked for them.
Your best bet is to talk to a propellor shop and get them to help you come up with the right prop for you boat. Sizing a prop is more an art than a science, since there are a lot more variables than just transmission gear ratio, engine HP, boat displacement and prop size and pitch that go into it. Dave Gerr's The Propellor Handbook is an excellent book for you to read on this subject.
Horsepower is 20 hp , aperture restriction does preclude the use of a folding prop, present prop is 13" ( not sure of the pitch , though) ,gear ratio is what comes with the "standard"( is there such a thing?) tranny that usually comes with the 20qm.
I would suggest that you contact a prop shop and give them your specs.
I would also check out Campbell Props. Very good reviews about their props from several members of this site.
http://www.westbynorth.com/
I would also check out Campbell Props. Very good reviews about their props from several members of this site.
http://www.westbynorth.com/
The best answer is to let a professional prop shop do this for you.
1- Your engine manufacturer wants to see the engine be able to turn max rated RPM at wide open throttle usually within +/- 100 RPM or so.
2- Your existing prop may be able to be re-pitched but let the prop shop do the calculations and tell you if it can be. If you need more than about 2" of pitch change you'll likely need a new prop.
3- Sizing a prop is usually a NO CHARGE feature when buying a new prop or re-pitching.
4- Even professionals have a tough time hitting the +/- 100 RPM range so make sure you get a written guarantee they they will re-pitch or adjust your prop for no charge after they have done the sizing. Most any REPUTABLE shop will do this.
5- Trying to get accurate prop calculations off a forum can be an expensive mistake especially when most prop shops DO NOT charge for sizing when you re-pitch or buy a new prop from them.
6- Engines are EXPENSIVE so guessing with your prop calculations can cost you in the long run...
I am a firm believer that the massive number of plugged exhaust elbows we hear about is closely related to the improper sizing of sailboat props. Do your best to get your prop in-line with what Yanmar wants to see the motor be able to turn at WOT for RPM and you'll be in good shape...
I suggest you contact Dan Tucker at Flexofold North America [781.631.3190 amsales@flexofold.com] as they have a sale going on their props. If you send him the information the other posters referred to, he can tell you what prop will fit your boat. The quote for my boat was under $1000, and he indicated that through 4/23, he would extend that price to others using a similar prop.
Koolfrog:
I think the advice already given by forum members is good; namely get professional prop shops/manufacturers into the picture.
That said, for what its worth, my boat's specs are not radically different from those you mention for yours. I've got a Yanmar 2QM20 (the transmission ratio is 2.14 to 1 -- attached is a photo of my engine name plate which is on the right side of the engine as you are looking from the pully side towards the aft direction), 36 ft, 13,500 lbs displacement. The Hunter factory prop which I had installed until very recently was a two blade 16" x 15p. The Yanmar tach would max out at ~2500 rpm vs the name plate 2600 rpm rating. So the 16x15 was a pretty good match to the boat and engine. Considering your 13" way different than a 16", it's good you are giving this some evaluation. Maybe there are some clearance issues with your boat that limits the boat to a smaller size prop?
I recently installed a Campbell Sailor prop which Steve Dion has already mentioned in this thread. I've had only a couple of outings on it, but initial impression is a noticeable improvement compared to the 2 blade. Boat seems to move forward nicely with less noise/vibration from the engine, with more speed at a given rpm (but this also might because of the newly painted bottom) ... And most particularly, my previous severe reverse prop walk is now reduced to something a lot more manageable. As said though, early days yet with this prop. I've only been in reverse a couple of times.
I think the advice already given by forum members is good; namely get professional prop shops/manufacturers into the picture.
That said, for what its worth, my boat's specs are not radically different from those you mention for yours. I've got a Yanmar 2QM20 (the transmission ratio is 2.14 to 1 -- attached is a photo of my engine name plate which is on the right side of the engine as you are looking from the pully side towards the aft direction), 36 ft, 13,500 lbs displacement. The Hunter factory prop which I had installed until very recently was a two blade 16" x 15p. The Yanmar tach would max out at ~2500 rpm vs the name plate 2600 rpm rating. So the 16x15 was a pretty good match to the boat and engine. Considering your 13" way different than a 16", it's good you are giving this some evaluation. Maybe there are some clearance issues with your boat that limits the boat to a smaller size prop?
I recently installed a Campbell Sailor prop which Steve Dion has already mentioned in this thread. I've had only a couple of outings on it, but initial impression is a noticeable improvement compared to the 2 blade. Boat seems to move forward nicely with less noise/vibration from the engine, with more speed at a given rpm (but this also might because of the newly painted bottom) ... And most particularly, my previous severe reverse prop walk is now reduced to something a lot more manageable. As said though, early days yet with this prop. I've only been in reverse a couple of times.
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