Sailboat Props for Outboard Motors

[sunbeam2]

I want to get the most speed my engine can deliver on a sailboat.<br /><br />I have heard about Hi Thrust props and Hi thrust Motors<br /><br />What about re propping and existing 1994 Evinrude 8 hp with a hi thrust prop? Are they available?<br />What will it do for me??<br /><br />Reverse power is almost non existant on my engine no matter how much I rev it up.<br /><br />Will a hi thrust prop or a hi thrust engine make the sailboat go faster when you have to use the motor, like running from a thunderstorm??>

 

[phatmanmike]

Re: Sailboat Props for Outboard Motors

8hp is 8hp... no matter how large the prop.<br /><br />hi thrust motors are those such as the yamaha60hp, or the mercury bigfoots, but they are generally only available larger than 25hp, they do not make a hi thrust 8hp outboard.<br /><br />thats all i can tell ya , if you know the storm is coming and you can only go 6knots, id stay home and browse iboats.com

 

[ED21]

Re: Sailboat Props for Outboard Motors

I used to do a lot of sailing. I don't think I ever beat a t-storm home.<br />A 8 hp will power most boats up to about 25' to hull speed.<br />If you can determine RPM maybe you could reprop to optimum rpm. That should give more power forward, but I don't know about reverse.<br />One problem with sailboats is that their is a lot of inertia to overcome & outboards never seem to do that well going backwards. <br />Part of the reason I think is because of exhaust being pulled into prop.

 

[Seakindly]

Re: Sailboat Props for Outboard Motors

Sunbeam2 -- if you are going to keep your current motor -- buy the highest diameter and lowest pitch prop you can find for that motor. See what it does -- if you are not satisfied you will need to go to a yachtwin or sailmaster 9.9 or look into the high thrust motors from yamaha, merc or honda.

 

[jim dozier]

Re: Sailboat Props for Outboard Motors

Sail props (props with less pitch than standard) are simply there to allow the motor to reach operating rpm on a vessel that is only moving at 6-8 knots. IF your outboard was not reaching maximum operating rpm with the standard prop (which is likely on a sailboat) you might get another knot or two out of it. More likely you would simply be easing the load on the engine, running at a lower temperature, reducing carbon buildup in the engines and sparkplugs, getting better fuel mileage, and extending the life of your engine. Power in reverse may be better also. Also power into the wind will be improved, that is your speed won't be reduced as much in a headwind. Sail boats (or any displacement hull) have a hull speed which is the maximum speed attainable without getting on a plane. This is calculated with a formula and is heavily dependent on waterline length. Longer boats generally have higher hull speeds. If you are already achieving hull speed with your current setup, you won't be going any faster with a diffeent prop or a bigger engine. That said I strongly recommend that you buy a sail prop for your outboard on your sailboat. The motor will be much happier and in the long run so will you.

 

[Capn Mike]

Re: Sailboat Props for Outboard Motors

If I recall correctly, displacement speed: length (squared) X 1.3 = speed in knots; knots X 1.2 = mph. You can fool the formula with bulbous bows, keel and/or hull design, particularly on larger sail or power boats.<br />In your case, Sunbeam, observe how fast you're going at full throttle. If it's close to your theoretical hull speed, doesn't matter what horsepower or prop change you make, you won't go faster. Jimd is right, I believe; if changing props will get your rpm to its optimum operating speed, that's a good idea. But you won't go faster.

 

[rodbolt]

Re: Sailboat Props for Outboard Motors

we had a lot of sucess on the 4,5 8 9.9 and 15 mercs using the high thrust prop and the exhaust blockoff kits on the blow boats. the blade design allows for almost as much thrust in reverse as in fwd. a standard or even dumber"weedless" prop will sometimes blow out rapidly and allow your pretty pulpit to smack the pilings. usually the piling wins. give it a try its only money.<br /> winds free and everything else otta be

 

[ivar]

Re: Sailboat Props for Outboard Motors

Yamaha's got propellers for that purpose , <br />I can't see the OMC engines don't have something similar. <br /><br />Yamaha Dual Thrust Plastic Propeller<br />Series R<br />Specially designed for sailboats and other displacement craft, Yamaha's patented Dual Thrust propellers are built to handle the job of pushing heavy loads through water. The hub is carefully designed to redirect exhaust flow away from blades, so Dual Thrust models cut through "clean water" for higher efficiency and better acceleration. Thrust is improved up to 70% in reverse and 10% in forward.<br />This propeller will fit the T8 and T9.9 models.