More power

[JON D]

I have a 30foot 1980 it has a 12 horse It has 2 blade prop would a 3 blade help where would I get one?

 

[David Foster]

Pros and Cons

12 horsepower will never drive it like 20!Three blades can improve "bite" - acceleration and other characteristics. But it won't add power to the equation. And three blades will slow you down (0.5 knots?) when you are sailing.Check the archives - there are a number of informative threads on this topic. I think the real conclusion is to get a good prop shop, and talk to them about the alternatives.DavidLady Lillie

 

[Bob Howie]

Props & Power

The answer to your question is simple and complicated. Yes, a 3-blade would help, but only some. No prop will totally compensate for being underpowered and 12hp on a 30' boat is underpowered. As to where you can get a prop, most prop shops handle such things and typically, a 13x13 3-blader, which is just about the most your boat's gonna be able to handle, is usually about $300 new. I've got a fancy one on my 78h30 that is 3-blade and uses some unique aero/hydrodynamics to improve it's efficiency and is connected by a 49" monel shaft to a 24hp Bukh diesel that I installed in lieu of a 9hp Yanmar YSM-12 engine last Sept and I paid $420 for it from Bay Props in Alameda, CA.Hope that helps. Questions?

 

[Bob Howie]

# of Blades v. Drag

I respect and cede David's point on a 3-blade prop slowing you down some -- a half of a knot in David's example -- yet I think that is a totally inconsequential concern because a badly-trimmed sail or an unmaintained, encrusted bottom will knock off more speed than a simple half knot. Besides, if a half of a knot is that big of a consideration in a cruising boat, sell the thing and go by jet!!!

 

[David Foster]

Half a knot is an hour longer

on an average 8 hour crossing of Lake Erie, or a normal 40 mile cruising leg.This kind of cruising richly rewards boats speed. So we try to keep our efficiency up however we can.DavidLady Lillie

 

[Bob Howie]

A half knot over a long haul

I agree that a little bit can make a big difference in some cases...reducing speed, say, under power, by a single knot with the idea in mind to get a better fuel efficiency or range over a 24-hr period with a max hull speed of 7 knots will add as much as 4 more hours to the proposed arrival time...provided, of course, there's enough fuel for 4 additional hours!!I think, tho, there are other considerations than a 2-blade v. 3-blade prop that are likely to impose more of a speed penalty than a single extra blade. I wonder, too, whether the folding/feathering prop debate considering the costs and maintenance required to keep the prop fully functional is valid. Here in the salt water of Galveston Bay, I can assure you that even the most rigorous efforts to the contrary still result in some bottom and prop fouling, ergo, additional penalities to speed, so that's why we all go over the side every few months with wire brush and chisel in hand to do a little bottom maintenance.Your points are well taken.