Jack plate...where should my reference come from?

[aeviaanah]

I am gettin ready to make a jack plate this week. I need to establish my low/high point. Any idea where a good starting point is in relation to cav plate?

Should the cav plate be equal height to bottom of transom at lowest point, highest point? Adjust up from there or both down and up?

Any ideas?

 

[smokeonthewater]

Re: Jack plate...where should my reference come from?

that depends on the boat and it's intended use.... for a flat water speed boat with an infinitely adjustable plate I'd say that the bottom setting should be about 1/4" below and go up to several inches above.

For an offshore fishing boat used in very rough seas you may want to be able to go a couple inches below


also generally, the more set back you have the more height you can have

 

[aeviaanah]

Re: Jack plate...where should my reference come from?

I'm putting a 15hp motor on a 12' mod v aluminum fishing boat. The boat is rated for 10 hp.

 

[aeviaanah]

Re: Jack plate...where should my reference come from?

this is my boat

this is the jack plate i will be building

 

[metriccrescentwrench]

Re: Jack plate...where should my reference come from?

You're probably just going to have to do a lot of experimentation, as I doubt that anyone has experience with the exact setup you're attempting. Just as a point of reference, with a 6 inch jackplate I run my prop centerline about 2-1/2 inches below the pad, which puts the AV plate well above the pad. However, you're hull is very much different than mine and we're worlds apart in power. The good thing is that your engine is relatively light and it won't be a big deal for you to move it up or down on the jack plate if need be.

 

[aeviaanah]

Re: Jack plate...where should my reference come from?

You're probably just going to have to do a lot of experimentation, as I doubt that anyone has experience with the exact setup you're attempting. Just as a point of reference, with a 6 inch jackplate I run my prop centerline about 2-1/2 inches below the pad, which puts the AV plate well above the pad. However, you're hull is very much different than mine and we're worlds apart in power. The good thing is that your engine is relatively light and it won't be a big deal for you to move it up or down on the jack plate if need be.

Thanks for the response...I am trying to minimize the amount of holes in my transom. I guess I could drill one set of holes and adjust the jack plate as necessary.

 

[robert graham]

Re: Jack plate...where should my reference come from?

Do you really need a jack plate on a smaller boat/motor set-up like that? You could just hang the motor on the transom with cavitation plate about an inch above the bottom of transom, save time, trouble, weight, expense$$? I mean what will you gain from this? Just curious.

 

[smokeonthewater]

Re: Jack plate...where should my reference come from?

Thanks for the response...I am trying to minimize the amount of holes in my transom. I guess I could drill one set of holes and adjust the jack plate as necessary.

Isn't that the whole purpose of having a manually adjustable jack plate? That's exactly why I suggested what I did.... start at or just below the keel and adjust up till you find your sweet spot.

 

[jacoboregon]

Re: Jack plate...where should my reference come from?

I realize this was already asked... why are you putting a jack plate on? Are you trying to put a long shaft on a short transom or vice-versa?

 

[aeviaanah]

Re: Jack plate...where should my reference come from?

Do you really need a jack plate on a smaller boat/motor set-up like that? You could just hang the motor on the transom with cavitation plate about an inch above the bottom of transom, save time, trouble, weight, expense$$? I mean what will you gain from this? Just curious.

Not sure, A few guys at work said I will benefit from one. It wont cost me anything, I get aluminum and hardware for free. As for the time, I enjoy fabrication. As far as the weight I think it may help because I am already heavy in the back, moving motor back a bit will help weight on front end. Farther out= more leverage thus more weight on front end.

Isn't that the whole purpose of having a manually adjustable jack plate? That's exactly why I suggested what I did.... start at or just below the keel and adjust up till you find your sweet spot.

Ok will do.

I realize this was already asked... why are you putting a jack plate on? Are you trying to put a long shaft on a short transom or vice-versa?

No 15" shaft on a 15" transom. Motor is the right size for the transom. A few guys at work said I will benefit from one. You dont think it will help at all? I thought It would be nice to have some adjustment. Im new at this so any suggestions will help. Thanks. First boat, first motor....I figure if Im going to do it, i better do it before drilling holes thru the transom. Still waiting on motor, should be here this week.

 

[smokeonthewater]

Re: Jack plate...where should my reference come from?

moving it back won't help with a stern heavy condition but rather it will have just the opposite effect.... smart tabs WOULD help tho

 

[jacoboregon]

Re: Jack plate...where should my reference come from?

Smoke is right on about the tabs. Before you go through the time of fabricating and installing a jack-plate you may want to adjust the hight and trim on your o/b first. You can search the subject here. Start with the anti-cavitation plate near level with the bottom of the boat and adjust up or down until it is right at the surface while traveling on plane. Adjust the trim out or in to keep the bow at the right attitude while on plane (slightly bow up). You may want to start with the 3rd hole out and adjust from there. You should have plenty of room on your transom to raise the motor if needed. You should have 5 or 6 settings on the trim.

 

[ezmobee]

Re: Jack plate...where should my reference come from?

moving it back won't help with a stern heavy condition but rather it will have just the opposite effect.... smart tabs WOULD help tho

I was thinking this also. You're overpowering a 12' and now you're going to set the motor back even further? Doesn't seem like a great idea to me.

 

[aeviaanah]

Re: Jack plate...where should my reference come from?

Ok it sounds like the jack plate isnt a good idea for this setup. Ill skip out on it then. Thanks everyone!