MacGregorSailors.com

Hi need a bit of advice..I have just purchased a new 26m fitted with a new evinrude 90 hp etec outboard.On delivery the outboard had a 15 inch pitch by 13 7/8 diameter sst stainless prop..Top speed was 16 to 17 knots at 3800 rpm.Not good!!! The dealer gave me an 11 inch pitch same diameter 3 blade alloy prop to try...The result was same top speed but revs up to 5000 max...Very disapointing..The dealer has done a computer health check on the engine ..All is ok..The outboard is a 20 inch shaft model and the height on the transom is such that the top of the outboard bracket is about 40 mm above the top of the transom..I feel the motor could be raised at least one hole ..Has anyone got any thoughts re this dissapointing performance or advice on the best prop for this motor and what sort of performance it should give..These figures are without water ballast!!!! :)

Mod's edit: Corrected to 'sentence-case' and expanded thread title -fc

I first assume that the boards are up, Good. Did you empty the ballest?

What was the conditions? Head wind, waves, lots of spray in your face or none?

Let's see 17 knots to mph = _______ you should be getting a little more. Good on the smaller prop.

YEP BOARDS AND RUDDERS UP ...NIL WIND ..NIL CURRENT..SPEED CHECKED ON 2 GPS UNITS..DEFINITELY NOT PERFORMING WELL..EMPTY BALLAST TANK...???????WHERE TO NOW???? THANKS..

17 KNOTS IS AROUND 19 MPH...NOT GOOD FOR 90 HP

I think you have too much pitch. Need to get the rpms up to max out HP from the motor. 10 or 11 pitch for the 50 hp works well. I would think you want around 6200 rpm or something like that. check the HP vs rpm curve for your motor and get a prop that puts you at the peak of curve.

Well, lets see...
You are about 13 feet ASL, so that's out.
It has been mid 20's deg C, not too hot to affect engine performance.
I have read that 14x11 or 14x13 is good for your motor.
I would raise it up a hole, supposed to improve top end.
I would also get a wedge as recommended by some and used by BWY to improve planing off and perhaps top speed as well as just giving you more trim adjustment.

Cheers

I found the information, and advice from the website linked below to be extremely helpful when I first got my boat.

http://www.kencook.net/Setupart.html

if your prop looks like this and is a full 14" x 11 or 13 pitch, then there's something else going on.
make sure that your prop has alot of water surface area (aka...big dog ears).



remember, you're pushing a "waterbago".

Bob T.
"DaBob"
'02X w/ '04 90-TLDI (14" x 11 pitch)
Dinghy Motor: '06 2.5-Suzuki

I have a 2006 75 etec on my X i get 24 mph at 5000 rpm no ballast and bottom paint. i use a 14X11 prop, I think it might be the new Pontoon prop. I am running the standard oil, not the 100. and 89 octain gas (12 gals) I think you nave a issue, but i am not sure what it is. you might want to check the mounting i am about 1 inch below thr transom.

How is your boat trimmed? Is it down too much at the stern? If it is, you need to trim it level. A boat that is trimmed stern heavy is inefficient. To gain maximum efficiency, the boat needs to plane. When a boat is stern heavy, the engine tries to force the stern down even further, so reducing efficiency and speed. With a 90HP and full tanks aft there may be too much weight. Try adding weight forward of midships nearer the bow and see how the boat reacts.

jasper wrote:How is your boat trimmed? Is it down too much at the stern? If it is, you need to trim it level. A boat that is trimmed stern heavy is inefficient. To gain maximum efficiency, the boat needs to plane. When a boat is stern heavy, the engine tries to force the stern down even further, so reducing efficiency and speed. With a 90HP and full tanks aft there may be too much weight. Try adding weight forward of midships nearer the bow and see how the boat reacts.

I just had another thought. Perhaps, installing one of the hydrofoil stabilizers on the market may help. They work by deflecting the discharge current from the prop in a downwards direction and resulting in the stern being pushed upwards, allowing the boat to trim level and increase efficiency and speed. Maybe another lister has tried this.

hydrofoil stabilizers ?? So far, no good reviews on this board.

Check the condition of your prop. Is it bent of have dings? A little of this can cause a lot of problems.

THANKS ALL FOR YOUR SUGGESTIONS...IM ARRANGING TO LIFT THE MOTOR ON THE TRANSOM TOMORROW..KEEP YOU POSTED..WILL ALSO TRY SHIFTING WEIGHT FOWARD TOMORROW...THE BOAT IS VERY NOSE HIGH AT TOP SPEED AND REALLY FEELS LIKE ITS NOT PROPERLY ON THE PLANE. DOES ANYONE KNOW WHERE TO PURCHASE A WEDGE PLATE TO MOUNT THE MOTOR MORE TRIMMED DOWN TO TRY TO LOWER THE NOSE????

FURTHER TO PREVIOUS..DONT REALLY WANT TO FIT HYDROFOILS IF I DONT NEED THEM...IT SEEMS OTHER BOATS WITH SIMILAR POWER ARE DOING MUCH BETTER SPEEDS WITHOUT A FOIL FITTED SO HOPEFULLY I SHOULD GET MINE PERFORMING BETTER WITHOUT HAVING TO RESORT TO A FOIL..I HOPE!!!

CURRENT PROP IS VERY SIMILAR TO THE ONE IN DABOBS PHOTO..13 7/8 DIAMETER AND 11 INCH PITCH WITH BIG BLADE AREA AS IN PHOTO..I WILL TRY TO GET SOME OTHER PROPS TO TRY AS WELL.THANKS ALL FOR YOUR HELP!!!