New motor setup

[wildfire]

I just purchased a new motor and have a few questions on its/boats performance. I went from a 30 hp tiller no trim and tilt to a 40 hp with trim and tilt. The boat is a Lowe 17 Husky with an 82 inch beam. The Yamaha 40 tiller I have on it now has a 10 x 15 aluminum prop.<br /><br />The max rpm I get out of it is 4200 with the trim in the down position. I called the dealer and told him I wasn't getting into the suggested 4500 - 5500 rpm range and he said I need to trim the motor up until it almost blows out. I tried this and the boat porposes BAD. <br /><br />Any suggestions? I get about 27 mph in the trimmed down position.<br /><br />Thanks

 

[AMD Rules]

Re: New motor setup

I called the dealer and told him I wasn't getting into the suggested 4500 - 5500 rpm range and he said I need to trim the motor up until it almost blows out.

Thats a dealer to avoid next time. Sounds like they simply did not want to help you, likely due to the fact that they are busy at this time of year. The proper solution to obtain rpm requirement is to ensure that the anti-ventilation plate is near flush or slightly higher than the bottom of the keel at the transom, and then to re-prop as required.<br /><br />If possible, verify your tach for accuracy. You'll probably want to go down a pitch or two to get the rpm into desired range. Find a dealer that is willing to work with you, and hopefully let you try other props until you find the perfect match.<br /><br />If you need the current prop for top end speed, you may be able to gain some improvement (reduction in porpoising) by installing trim tabs. Either way, you need to get the rpm into recommended range to ensure motor is not overworking.

 

[AntsGrady]

Re: New motor setup

I tend to agree with the dealer to an extent. The higher the motor the better the performance but you have to find the right trim. If you're porpoising it sounds like you are trimmed to high. Find a happy medium. Smart tabs would be a good thing I'm sure but work on the trim first then decide.

 

[b.gagnon]

Re: New motor setup

sounds to me like you have the wrong prop.

 

[wildfire]

Re: New motor setup

Thanks for the suggestions. I'm going to get out this weekend and play with the trim some more. If that doesn't work should I consider a hydofoil? <br /><br />How would the wrong prop make it porpoise? <br /><br />I'm realatively new to this game of boat set up. The new motor is about 40 pounds heavier than the old one.<br /><br />The old motor had a hydrofoil on it and I never tried it without so I don't know if it would of porpoised without one.<br /><br />Thanks

 

[Solittle]

Re: New motor setup

If this engine is not broken in yet (you said "I just purchased a new - - -) I would get that behind you first. Your owners manual should give you the break-in procedure and the max rpm when broken in. You should be able to run at rated rpm at WOT. And yes you will need a different prop. Your dealer should supply this at no charge to you with a new engine.