Jackplate size why it matters

[pmgoffjr]

The internet. Vast stores of knowledge at ones fingertips.
Too bad most of it is wrong.
The long conversation on plate size warrants it's own topic.
This is for Mt. Home champs, NOT TN champs, apples and bananas, I'll get to that later.
LOOK at your boat. No I mean get on the ground and look at the angles, the distances, the measurements. It's all there with a purpose. WHY does your boat ride like it does? WHY does it handle and turn like no other? It's all in the back 4' of your boat.

The one we'll discuss today, there is a distance from the rear of the pad to the transom. That distance was tested to give the optimum distance to perform, maintain control and handle. WHY??

The why: anything moving through water creates a swell behind it. Easy enough to see. Your optimum distance is exactly at the top of that swell. But the swell will move depending on speed. So you want to be in front of the swell all the time, and NEVER be behind it at any time.

When you push the pivot point (your prop) behind the swell, very bad things will follow, and on a champ hull that very bad thing is you'll lose the ability to maintain control. When the prop loses it's water contact, so will you. The first thing you'll find in too much setback, the boat gets "Icy" feeling, you're turning the wheel, but the boat isn't reacting to it.

THAT will be your first clue you're in the range to bow hook. That happens when the keel has more control than the prop does, like jamming the front brake on a motorcycle. If it's in a turn when it takes over, the result is a 180 degree end swap. On a 1-10 scale of bad stuff that happens, bow hook is a solid 8.5, only things worse is blow out or collision.

And...all that for why? Because some internet expert told you to hang a 12" on your champ because that's what HE runs on his nitro?

And....and....your net gain mph will be....zero. We've already rigged just about everything on just about anything. Follow the path already taken. It's a lot easier.

[rojoguio]

Pat, you beat me to creating the thread. While eating I was mulling over the problem myself. I'm a Marine Engineer so first place I went was LCG (Longitudinal Center of Gravity) for those who don't balance ships. Anyway, I use PC925 Odyssey Batteries, 4 of which are 88#'s total. Figuring MH Ark designed a 171 for 3 batteries around 27 series or so. From the calculations I could not see why the negatives were developing. The 80# Ultrex trolling motor I have for the bow is over 70#'s itself. Heavier than the 70# trolling motors of 1996. So I could only think it had to do with the Fulcrum distance with the prop to running surface and prop position in the water column. I don't know how long it would have taken me to take the swell itself into consideration but your post concerning prop relationship to boat swell needs to be made a "Sticky". Very Kind Regards, Thanks for sharing Your experience with us.

!

[ChampioNman]

To add to Pat's comments many Mt. Home Champs run better with out a plate. I ran a 201 with a Gt 150 on the back and could feel it get up on the pad all the time. I hung a new motor on the back and of course decided I need a plate. Hung a 200 on the back along with a 9' RJ plate on it. Ran well until I put a 225 HO on the back and then it fell flat on it's face. Had to change the backing plate to 7.5" She runs very well now., sometimes it is better to leave well alone.

[Radeleur]

I agree Pat. I just measured the setback on my 89 201 and it is already at 7 1/2 inches just in the hull alone.

[1bluemcm]

The "why" is important, and I am glad I now know much more about the "why" of JP size on Champs, thanks for the pearls of knowledge Pat.

This group in particular has such a wealth of knowledge, good knowledge not garbage, that I have had no problem going with the widely accepted recommendations when it comes to setup.

There is obviously the potential for a very bad handling outcome with too much setback, i.e., good chance of loss of control, what's the main downside of not enough, mainly limited performance? Do you actually increase margin of safety any by having less than optimal setback? In other words if you have too little setback, could that actually prevent things like a bow hook to any practical degree? How does not enough setback negatively affect handling? Mainly rhetorical questions here.

[86 inches]

I've always wondered how mine would have handled without a jackplate with my original 225 Venom. I ordered it new with a 6" plate and for years it seemed fine. At one point I added some 2" spacers and I think the handling and performance may have decreased somewhat. It was a challenge getting it set up with the new G2. For anyone that might do that, mounting it straight to the transom is the ticket. That gives it a 6" setback which seems perfect, though there is no way to know how it would perform with less. I know for a fact that adding a traditional 6" plate makes it worse.

[pmgoffjr]

The "why" is important, and I am glad I now know much more about the "why" of JP size on Champs, thanks for the pearls of knowledge Pat.

This group in particular has such a wealth of knowledge, good knowledge not garbage, that I have had no problem going with the widely accepted recommendations when it comes to setup.

There is obviously the potential for a very bad handling outcome with too much setback, i.e., good chance of loss of control, what's the main downside of not enough, mainly limited performance? Do you actually increase margin of safety any by having less than optimal setback? In other words if you have too little setback, could that actually prevent things like a bow hook to any practical degree? How does not enough setback negatively affect handling? Mainly rhetorical questions here.

Until '95 when I got my first 202 we were not allowed to run a plate on our demo boats. They were considered unnecessary and detrimental to handling. Now, that said, I've always had issues with rules, so I'd smile and nod, and then go do whatever I wanted. Just made sure I pulled the plate off when I rotated the boat back to the factory.
Even a 6" plate will affect handling, the harder you run it, the more obvious it becomes. When you watch the demo video, you'll see no plates on those boats, because...if you try the 60 mph U turn with a plate, you better be paying attention if you have a plate, it'll spin out (bow hook) without a plate, you couldn't make it hook. Really hard turns at WFO, you'd feel the boat wanting to slide around a bit, without the plate, it was on rails.

So doofus, why did you put a plate on at all? Because there is a difference when you load it down on tournament day. 3-4 mph on a 184/175. And #2 on my priority list was to never ever get passed by a Skeeter. So I ran one to make sure that never happened.

[1bluemcm]

I think I've experienced that slide effect a couple of times with my 191/8" plate, but I'm not trying to get hurt either so I back off. I realize the limitations that automatically come with me behind the wheel....not that I'm not trying to improve.

The essential complete inability to hook one without a plate, does that boil down to the fact that the trailing swell can never get ahead of the prop, or is there more to it?

Good to see you had your priorities straight.

[Radeleur]

After having a recent experience with 2 different fx20 skeeters I will always have a plate just not a huge one. Both the trims failed on the same day. I was a coangler in 1 and my buddy owned the other. One we had to drag up the ramp dragging the skeg and manually life a big 250 at the top of the ramp and the other we just raised the plate and drove it to parking and lifted it there.

[pmgoffjr]

If you haven't studied the demo video, don't just look at the boats zooming around, study the drivers, pay attention to the actual maneuvers, the trim angles, how the boats react to changes. Now look at the very end of the video, you'll see me doing a full knucklehead spin out (bow hook) You can make it to it by going full lock turn and not shutting off the throttle, you'll eventually break the prop loose from the water and there you go. DO NOT try this at home, it's not fun, it's not pleasant and it's really easy to get slung out.

But, that's a bow hook.

[MMosher]

As always good stuff Pat. Ran my 202 flat back on the transom for 4 years before putting a plate on her.

[momarkmach1]

Pat is the king of kings ! Such a wealth of experience and valuable information , I appreciate you buddy !