Jackplate installation raises WOT RPM

[Extremeboating]

This can't just be at random, but on both boats I've owned (both tin) I've noticed that the moment I install a jackplate, even before I started raising height I gained top end RPM at full wide open throttle by about 150 extra. Has anyone else ever experienced this? I've searched on the topic before but have never found any definitive response on the topic outside of people raising theirs to get RPM gains.

[Highcentered]

Has your top speed increased also? Would suck if you suddenly developed prop slip. Also, I wouldn't play with jack plate hight much if any while running down the lake. I've heard that playing with height like that can cause a prop to not stay hooked up good. At least that's what Rick Pierce of BCB says. Nice looking rig too. When I first saw it last year when looking for my next boat the shape of the front deck on that short boat caught me off guard, lol. Crazy how beam forward that thing is. Sadly, the rod box quickly took it off my list with the organizer that didn't look like it could be removed and wanted Seadek. I have a sickness and have 16 setups in the box of my H18. 12-13 was all my old 175txw could hold.

[Extremeboating]

Has your top speed increased also? Would suck if you suddenly developed prop slip. Also, I wouldn't play with jack plate hight much if any while running down the lake. I've heard that playing with height like that can cause a prop to not stay hooked up good. At least that's what Rick Pierce of BCB says. Nice looking rig too. When I first saw it last year when looking for my next boat the shape of the front deck on that short boat caught me off guard, lol. Crazy how beam forward that thing is. Sadly, the rod box quickly took it off my list with the organizer that didn't look like it could be removed and wanted Seadek. I have a sickness and have 16 setups in the box of my H18. 12-13 was all my old 175txw could hold.

Yeah overall top speed capability has gone up in both instances but I've usually had to raise up height in order to find the right top speed. I don't know, it's just weird how I've always heard people say that wide open RPM should not change if the only change is the jackplate and you aren't raising it, but in both instances I found that without even having to raise the engine my RPM was increased by between 100-150, usually 150.

My sweet spot that likes to run at speed is in between 2.25-2.5 inches. My rig seems to like it when I raise the plate and water pressure is well within spec for this motor for sure. The prop doesn't seem to care that it's up high either because it just handles turns without blowout at all at any point.

I agree, the shape of this thing is very different than your average sub 18 footer. Especially the width of the deck. It's definitely a spoiling sort of thing, but makes the rig super stable in the water while just floating along. Definitely one of the more unique features of this thing which drew me to it in the first place. The engine size capability of it and the fact I knew I could make it fit in my garage with some quick work using some simple sockets and a rachet was the icing on the cake.

[GeauxTide]

Typical setback on a JP is 6", putting your prop in cleaner (less disturbed) water. I experienced the same thing. I had a 6" manual on a Lowe Stinger 18HP. Only gave 2mph.

[Extremeboating]

Typical setback on a JP is 6", putting your prop in cleaner (less disturbed) water. I experienced the same thing. I had a 6" manual on a Lowe Stinger 18HP. Only gave 2mph.

The cleaner water thing makes sense as to why it would raise RPM all other things being equal before any sort of adjustment. My stinger seems to love the jackplate and performs like a champ in every category using a 3 blade Tempest with it.

[GeauxTide]

Don't know if your hull is pad or semi-vee, but going to a 19" Spitfire X7 brought my hull to life.

[blkfalc4]

A JP raises the engine naturally even when using the same engine mounting holes.

[Ted-LA]

It would seem that cleaner (less disturbed) water would allow the prop to have a better "bite" and produce lower RPM if there were no other dynamics involved. I tend to think the leverage provided by the additional setback lifted the hull out of the water with the same or possibly less trim. This should reduce drag while increasing speed and RPM. Running the prop in cleaner water allows for potential performance gain by optimizing engine height.

[Extremeboating]

Don't know if your hull is pad or semi-vee, but going to a 19" Spitfire X7 brought my hull to life.

Mine is a legit pad on the bottom.

[bassfisher444]

More setback moves your pivot point back and gives you more bow lift which translates to more speed and RPM.