Motor Height

leachy · #1 10-04-2012, 12:55 AM

Hi All

I have just fitted a new Solas prop to my 25hp Yamaha. I just wanted to make sure the motor height is exactly right (need to get the best out of 25HP, not much to play with). On my motor there are two sort of cavitation plates, one directly above the prop and another about 5cm above that which has bolts on the bottom side and faces more forward.

http://www.yamaha-motor.com.au/sites...htbox/25CV.jpg

At the moment the water was just touching the bolts of the top cavitation plate. I am planning on raising the motor a bit more but I was wondering just how high to go. I have set it at the moment with the top of the main cav plat about 5mm below the bottom of the hull. The motor has a Hyrofoil fitted, triangle shape one with down turned tips, this means that these tips will now be out of the water. Most of my running is straight line with not much in the way of fast turns as I use the electric once I get close.

I am running out of transom height and don't want to drill any on necessary holes for the motor.

Regards
Leachy

seamonkey · #2 10-04-2012, 01:02 AM

You want the cavitation plate which is the first plate above the prop to be level with the bottom of the hull as a starting point.

The foil should only come into play when getting up on the plane anyway and once under way should pretty much be skimming over the top of the water surface.

So up 5mm if your measurements are correct.

smky

leachy · #3 10-04-2012, 01:20 AM

Thanks that what I thought but I have to try and build the transom up about 60mm, the screws are just on the top of the transom and I didn't really want to drill it just yet, but worried about the motor falling off the back.

Thanks for the advice.

seamonkey · #4 10-04-2012, 01:27 AM

Alloy hull I guess? It's pretty cheap to have a block welded on the top edge. Much safer and looks better. Or google "transom extender". There's some good examples of what needs to be done.

smky

leachy · #5 10-04-2012, 01:38 AM

Thanks and yes its alloy. I have worked out what I can do but just wanted to be sure it was right before I drilled it, dont want it to look like swiss cheese.

Danmaso · #6 10-04-2012, 02:29 AM

Quote:

Originally Posted by leachy

Thanks and yes its alloy. I have worked out what I can do but just wanted to be sure it was right before I drilled it, dont want it to look like swiss cheese.

Leachy what size prop did you go for? pitch?

leachy · #7 10-04-2012, 03:11 AM

I went for a 12" pitch, which is standard the diameter is slightly larger 10 1/4" (standard is 9 7/8"). The new prop has more cupping on the edge, makes a big difference