Tell me about jack plates

[wired247]

Ive never seen one in person and Ive never used one. Why should I think about getting one. What will moving the prop up and back do for me? What will I lose for a ski/under 60 mph boat.

[transomstand]

What will I lose for a ski/under 60 mph boat.

Whatever you spend for the jack plate:D

Speed is always the result of a combination, not an individual component. Even without knowing what boat you have, to make significant changes in speed, you'll be making many changes.

[wired247]

I have a 1981 checkmate enticer That Ive been dragging around since 1981. It currently has the original crank rated 90. Ive installed 140 HP heads to get the compression up a bit and a set of 1 3/8" carbs off a 175 XP. Ive got two props. One is a 17 pitch 4 blade stainless Solas prop. It tops out at 46 mph GPS with the 17 pitch. I also have a 19 pitch OMC stainless prop that tops out 50 ish on the GPS. Both are on the highest position on the transom. The 19 pich blows out of the water at anything over 1/2 up on the trim gauge.

I'm currently building a 81 vintage 140 with milled heads, fiber reeds, 1 3/8" carbs, squared ports etc. I'm looking for an honest 140 HP at the crank and I'd like to be able to hit 60 MPH with a 23 pitch 4 blade stainless prop. Sounds do-able to me on HP alone. Ive heard all the wonders of jackplate but I'm not sure that its all that because Ive never seen or used one. Might be the greatest thing ever as some have suggested but . What I am concerned about the drawbacks. What are they?

[Ron V]

Biggest advantage on your rig is that it will allow you to fine tune the engine height. The setback might help a little bit since Checkmates don't fly like a Hydrostream, Allison, etc. But to be honest, on your setup a jackplate isn't going to be the component that gives you the magical 5-10 mph (in fact no single factor will). The "slower" rigs don't respond as radically to minor changes. I really don't see any drawbacks other than you might need to have your cover refitted if you have a cover that goes over the motor, and it will put a little more strain on the transom. Is it worth it? Well, I saw zero advantage on my 50 mph V-4 powered rig, and even on the setup that I'm running now, it would be hard to truthfully say that I've gained more than 1 mph. When I first rigged the V-6 on the boat, I bolted it right to the transom and guessed at the engine height, and it ran 78-79 mph on the speedo with a prop that was beat to hell. With custom prop work, trying different props, adding 6" of seetback, and playing with the engine height, it finally has managed 80-81 mph (speedo) on a perfect day. BUT - you can set it up for top speed, and then still drop the motor down to bury the prop for pulling skiers. And there are "possibly" a couple of top end races that I wouldn't have won without the jackplate and prop work.