Prop torque.....

[Pete7]

Tim, please before you go drillin any more holes in that transom rule out other possible causes. Lurcher made a good point and worth getting the tape measure out.

What is the round mark in the middle of the the transom? has this boat been fitted with twin engines and then converted to a single ? Whilst you have the tape measure out what is the height of the transom in the middle ?

Take the prop off and look down the end, there will be a part number and prop size.

what happens at 5000 revs ? what are the maximum revs ?

Pete

[Tim M]

This one is a bit more clear - shows the old 75 bolted in the same holes. I'll go and measure the boat shortly....

[Seaharrier]

Most Eagles i have seen here in Belgium are fitted with an 115 HP engine and some with 150 HP engines.

The ones with 115 HP engines are mostly using 18" prop's. The ones with 150 HP are using 21" props.

Overpowered with a 115 HP shouldn't be a problem. If I remember well, someone has won the French championship's almost 10 years ago with an Eagle. They fitted a heavily tuned Mercury on it's transom. It had more or less 240 HP.

[blufin]

hi tim
as pete says get out the tape. the eagle hull is rated for 115hp so your engine should be no problem to it. i had one a few years back that i put a 130 V4 yam 2stroker which weighed 167kgs i think. it ran straight and true to early 50 plus mph with a 19" stainless prop. my engine was offset about 11/2". superb boat, great fun !
gerry

[Tim M]

An update:

The prop is indeed a 17 inch pitch (14 diameter). I've done some measuring and the engine is dead center, at 90 degrees on the transom. I was hoping to take the boat out today to check the max revs but the weather isnt really ideal so it'll probably be Wednesday now.

Having looked at it some more it seems that if I want to move the engine down at all not only am I going to have to drill new holes but I am also going to have to cut a chunk out of the top of the transom.

Pete: yes the boat did have twin engines on at one point. I understand they were both short shaft and that the transom was build up again after they were removed in order to accomodate a longshaft (the mariner 75). This would explain why the transom is a bit of a weird height.....

[Pete7]

Originally Posted by Tim M

The prop is indeed a 17 inch pitch (14 diameter). I've done some measuring and the engine is dead center, at 90 degrees on the transom.

Good.

Originally Posted by Tim M

Having looked at it some more it seems that if I want to move the engine down at all not only am I going to have to drill new holes but I am also going to have to cut a chunk out of the top of the transom

Actually I am going to suggest the opposite way. Osprey always built 21" transoms for single engine boats. So if a long shaft engine is 20" then the anti ventilation plate at the back of the engine should be 1" above the very bottom of the hull. If its lower then you need to move it up. An ali prop should run 1" up a transom although you will have to trim in on tight turns to avoid ventilation.

This is a 21" transom, the Yamaha ventilation plate sits just above the bottom of the hull and it goes well all be it with a S/S 19 prop.

I think Jimbos right, keep your eyes peeled for a 19" prop.

Pete

[BogMonster]

Originally Posted by Pete7

Good.
An ali prop should run 1" up a transom although you will have to trim in on tight turns to avoid ventilation.

Mine does that a lot, the plate is a bit above the hull and if you open the throttle any amount on a tight turn with the engine trimmed out you get lots of revs and froth! Trim the engine in a few notches and it will whistle round in circles with about 45 degrees of bank on, or it feels like it anyway. For some reason doing this appeals to the little boy inside me, must be still at the silly stage of boat ownership I guess