angle of boat motor

[bke]

I was wondering are the rpms affected depending on how the motor is trimmed?

 

[nlain]

Re: angle of boat motor

yes. bring to 3000 rpm, trimmed all the way down, verify speed and rpm, start to trim up a little at a time, you will see speed and rpm increase to a point. when they do not increase anymore you are at the best trim to get the most. Trim up anymore, lose speed, rpm may increase due to being to high up and trying to come out of the water.

 

[Philster]

Re: angle of boat motor

With my motor trimmed down/in, I guess I am good for 4000 RPM or less. Trimmed out/up is the only way she'll redline to 4800, because she's lifting the hull out of the water like this, and that removes a massive am't of resistance. I believe it directly and indirectly affects the prop, too. For planing hulls, and to different degress depending on basic design, it holds true.

 

[bke]

Re: angle of boat motor

I thought it affected the rpms. The other day when I was out on the lake I had the motor trimmed in and the front of the boat was plowing and I was still running around 5200 rpms.

 

[Philster]

Re: angle of boat motor

Do you have a 2-stroke motor that is under-propped and has a 6000 RPM redline? Can you tell us what kind of boat, motor, etc you have and what its performance is trimmed out/up? It's all relative.

I had a 2-stroke motor that redlined without the motor trimmed up, because there was no trim on the boat! But if that 115hp, 2-stroker had trim control, I could have run a bigger prop, trimmed her out and gained some MPH. If I never changed the prop but had trim controls, I would have blown redline for sure.

 

[rockyrude]

Re: angle of boat motor

Agree with Philster, if this a 2-stroke check your prop, if you get her up on plane you will easily cross 6000 rpm. Do it often enough and they become handgrenades.

 

[bke]

Re: angle of boat motor

i have a 17' 1999 tidecraft trophy angler fiberglass boat. It is rigged with a 2001 mercury 125hp with a ss prop and the prop is a 25p. I was only getting roughly 5000 rpms out of it and the pee hole was plugged a little after I blew that out the the rpms go up to at least 5200. The motor says 5250 for max rpms. I know one time I had the rpms over that.

 

[Philster]

Re: angle of boat motor

So, if she pulls 5250 with the motor trimmed down or set down, if you were able to trim it out, she'd over rev.

 

[bke]

Re: angle of boat motor

do I have to get a new prop from keeping it from over reving

 

[rockyrude]

Re: angle of boat motor

That is the generally accepted remedy. The trick is to figure out what pitch to get. Every 1" more pitch is about a 200 rpm drop.

 

[nlain]

Re: angle of boat motor

That is a yes and no question. Pull back on the throttle and keep the prop you have, you do not want to run wot all the time anyway. Go up a couple inches in pitch and maybe get a little more speed out of it. You need to try and find some place that will let you test props before you buy, otherwise it could get expensive trying to find the right one.

 

[bke]

Re: angle of boat motor

that was how the boat was set up since I bought it. I was thinking about keeping the prop and just not riding it so hard.

 

[rockyrude]

Re: angle of boat motor

Your wallet will like it too, you'll burn less gas that way too.