Adding Hydro Foil to Yamaha 8 HP 4 Stroke on 27 Catalina - SailNet Community
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post #1 of 27 Old 04-02-2013 Thread Starter
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Adding Hydro Foil to Yamaha 8 HP 4 Stroke on 27 Catalina

Has any one added a hydrofoil to help their sailboat plane at slower speeds to prevent the motor from being drowned?

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post #2 of 27 Old 04-02-2013
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Re: Adding Hydro Foil to Yamaha 8 HP 4 Stroke on 27 Catalina

not sure what you mean by plane, a CAT 27 is never going to plane. now with my 8HP outboard on my dingy it will plane. even with hydro foils on a 27 it would take about 1000 HP to make it plane

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Re: Adding Hydro Foil to Yamaha 8 HP 4 Stroke on 27 Catalina

Pretty much a non starter, methinks.....

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Re: Adding Hydro Foil to Yamaha 8 HP 4 Stroke on 27 Catalina

When i am at full speed the bow of my boat comes up a bit and the water line is very close to drowning my motor that is mounted in the transom motor well on my cat 27. I want to find out if by adding a foil if it will prevent my motor from digging deeper in the water and keep it level more?
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Re: Adding Hydro Foil to Yamaha 8 HP 4 Stroke on 27 Catalina

I think it just as likely to add drag and pull the stern down as add "lift" at 5 kts.
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Re: Adding Hydro Foil to Yamaha 8 HP 4 Stroke on 27 Catalina

Does anyone have this problem happening to them? any way to prevent it?
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Re: Adding Hydro Foil to Yamaha 8 HP 4 Stroke on 27 Catalina

If anything I would look at the angle the motor is sitting at and play with the tilt pin setting

Some boats just stern squat as they reach displacement speed I know my Cal 29 starts squatting at about 5 knots

Its silly take the Cal above 5.5 as at 6.5 knots it squats so BAD the scuppers let in so much water your standing angle deep and the fuel burn about doubles

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Re: Adding Hydro Foil to Yamaha 8 HP 4 Stroke on 27 Catalina

My transom well gets lots of water in it and the motor is close to the main motor. How low can a yamaha 8hp 4 stroke go to water level before drowning out?
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post #9 of 27 Old 04-02-2013
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Re: Adding Hydro Foil to Yamaha 8 HP 4 Stroke on 27 Catalina

Firstly it's not clear that you understand the concepts of displacement hulls, and hull speed.

Most sailboats have what are called displacement hulls, which are optimised for a mode where the water passes around the boat, instead of the boat riding over it like the planing hull of a speedboat. This means that your sailboat does not have the hull features which would make it plane - at ANY power (those features are large flat sections aft)

So you are stuck in displacement mode. A displacement hull has a concept called hull speed. This is the point where you are putting in more and more power, and not going faster. The power goes into the bow wave which gets bigger and bigger. As the bow wave gets bigger, the bow rises up it and the stern drops. This is your problem.

The fix is to go more slowly. I cruise at the point where the exhaust pipe is just above the water - about 6 kts on my boat.

I would expect your C27 to have a hull speed of about 6 kts, though you might get too much squat lower - as low as 5 kts.

You will also get much better fuel consumption cruising at the speed where the squat is small, as the power is going into moving the boat, not creating a huge bow wave.

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Last edited by MarkSF; 04-02-2013 at 03:10 PM.
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post #10 of 27 Old 04-02-2013 Thread Starter
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Re: Adding Hydro Foil to Yamaha 8 HP 4 Stroke on 27 Catalina

so there is no way to prevent this other then cruise slower?
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