1978 Hunter 27 prop and shaft

[Joe Carson]

I just purchase a '78 Hunter 27 with the one lunger Yanmar 8 hp 8D. It has a two bladed prop. To increase the speed, I am entertaining getting a three bladed prop. I'm yarding the boat in a few weeks to get the bottom done and would like to replace the prop at that time. Can anyone tell me what the prop/shaft specs are? Thanks.

 

[Doug T.]

Speed?

The prop has to be sized to the engine and to the boat. An 8HP motor and an H27 are simply never going to get you going very fast whether you use a 2-blade, 3-blade or 5-blade prop. If the prop's too big or the pitch is too large, the engine won't be able to turn it at sufficient RPMs to increase your speed. If you get a bigger engine, the hull speed of the boat will be the limiting factor. (Max hull speed is based on LWL for a non-planing hull.)Try www.michiganwheel.com. They have a prop sizing form you can fill out.

 

[Sue]

Yanmar

You can find this out by removing your existing prop and taking it in for replacement, they will be able to size it. If you need replacement parts for the engine the Yanmar dealer in florida is Mastry Engine Center2801 Anvil Street North, St Petersburg, FL 727.522.9471. They do not sell props however.

 

[David Foster]

How fast?

Hull speed is 6.2 knots. The 8 hp yanmar easily drives our '77 h27 at 4 to 5 knots. I have done 3.5 knots into 4 foot seas at the mouth of Sandusky bay.I'm looking for power to get me out of the marina, and to cruise at around 4.5 knots when becalmed.When the wind is up, I've got the main engine - the sails - to get where I want to go.To get up to 6 knots, and hold it against the weather, you will need a larger diesel, and a new prop - big bucks!The main advantage of three blades cited by those who have bought them (see the archives - really!) is more "bite." I think that means quicker acceleration which does make some sense. That could also translate to more average speed climbing the waves, but that is speculative.Finally, three blades will definitely produce more drag when sailing. a half knot is sometimes quoted. That's a 10 percent hit.Enjoy the boat - this is a really sweet model!DavidLady Lillie

 

[jcherubini]

Shifting into overdrive.

Remember that as people here have said, the prop and engine are mated together by the designer and ought not to be messed-with unless you know what you are doing about it. I've heard it said you should go down in pitch when you go up in blades and that makes sense.If you'll pardon my famous automotive analogy again, the propellor is correllative to the final-drive ratio in your car. Higher pitches are like lower rear-end gears-- they take longer to get up to speed but should go faster on the same HP (compare a Chevy 350 with a 4.11 to a Buick 455 with a 2.73). The potential problem is when the boat is a little ungainly or underpowered-- like the H27. Too much pitch and you may never get it up to cruising speed, meanwhile filling up the marina with black smoke whenever you try. And the added weight of a 3-blade prop is not going to help a low-powered engine, even a diesel. Sportscar wheels (and baseball bats) are made lightweight for this very reason.I would stay with 2 blades and possibly add an inch or so of pitch-- but not without listening to who's done it and hated it first.JC <--- big-block Buick person