Thread: Proper motor height

Originally Posted by catchNgrease

I had considered moving the TM batteries up there.. The bow is extremely light

Sent from my E6910 using Crappie.com Fishing mobile app

I've been there and done that more than once. It'll never act right until you weigh the front down. Just put some sandbags or water jugs in the front to try it out. You'll be surprised.

Dang just remembered I got 4 sandbags. They used to go to a pop up tent that probably made it Oz.

Sent from my E6910 using Crappie.com Fishing mobile app

You are not over propped on that rig. Under propped if anything. The optimax should like a 21p on that setup. The aluminum hull and light bow is not going to run like a glass boat. Also, high engine mounting is not always friendly. You may find better performance at a lower setting.

Originally Posted by sliderman

You are not over propped on that rig. Under propped if anything. The optimax should like a 21p on that setup. The aluminum hull and light bow is not going to run like a glass boat. Also, high engine mounting is not always friendly. You may find better performance at a lower setting.

Thanks fo the input. I have no problem dropping the coin for a new prop if needed. But I am a miser and prefer to have proof or solid recommendation

Update: I pegged it out and it hit 4950rpm. I gave it a small amount of trim and I heard the pitch change and it tried to take off but it only bounced.

Please coach me from here

Sent from my E6910 using Crappie.com Fishing mobile app

Here's some specs on the motor, says max RPM should be between 5000 - 5700 rpm...
MERCURY OPTIMAX THREE-CYLINDER 75 HP SPECIFICATIONS | Outboard Marine Technologies | Outboard Motor Parts NZ

Originally Posted by TheGrandPoohBah

Here's some specs on the motor, says max RPM should be between 5000 - 5700 rpm...
MERCURY OPTIMAX THREE-CYLINDER 75 HP SPECIFICATIONS | Outboard Marine Technologies | Outboard Motor Parts NZ

I read the data sheet. There is definitely more power left on the table. But when I trim up to get it the boat starts bouncing. If it's doing all it can do I except that. But I'm not convinced that's the case.

Sent from my E6910 using Crappie.com Fishing mobile app

Could try a hydrofoil. On my setup, 17' Tracker Deep V, 75hp Suzuki 2 stroke, it makes a big difference in being able to trim up more and keep the bow in check. When I tried it without there was no difference in top speed, but the boat was much more sensitive to trim, didn't take much at all to start porpoising. It'll also plane at very low speeds.

I get ~33 mph running wide open at 5300, I have a 15p aluminum now, have used 17 in the past and it was way too much.

Regardless, I don't think there's much more on the table with your setup, you might be able to squeeze a couple more MPH out of it, but don't expect much.

Originally Posted by catchNgrease

I read the data sheet. There is definitely more power left on the table. But when I trim up to get it the boat starts bouncing. If it's doing all it can do I except that. But I'm not convinced that's the case.

Sent from my E6910 using Crappie.com Fishing mobile app

Porposing is caused by the prop loosing "traction". Think of the motor as a lever with transom as the fulcrum. As the lower unit applies thrust, the bow rises. Ideally, the traction starts to gently "slip" so that the bow is kept at a constant level height. In a porposing situation, the prop suddenly breaks traction, the bow drops down, the prop then regains traction and the lift process starts all over again. The hard part is finding out why that prop is breaking traction. Sometimes it is a hook in the hull (which you can never fix). Sometimes it needs height adjustment. Sometimes it needs a prop with more cup or blades. That is where the experimentation comes in. I wish you luck.