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Performance Results - Skid Plate Installation = 30% Hole Shot Improvement #4409898 01/27/10 04:39 AM
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mcdil Offline OP
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Boat: Gambler 2000 Intimidator
Motor: Merc 225 EFI with Brucato Injection
Prop: 25" Tempest Plus
Trim Tabs: none
Jack Plate: 6" Detwiler on Gambler 4" set back (10" overall) - standard Gambler set up 10 years ago
Extras: Bryan's Foil (Installed several years ago)
Problem: Prop is too small of a pitch for top end performance, yet it still has trouble getting out of the hole with two aboard and livewells full. If it does come out without intervention, it takes about 6 1/2 seconds for the front to drop. For about 4 seconds of this time, forward visibility is eliminated. If the boat doesn't come out on its own from a dead stop due to hot weather, slick water, or power loss due to extra back pressure from the exhaust relief port going under water, the passenger has to walk up front in order to get the boat on plane. It will not come out unless that happens as the rear end is sucked down permanently due to the jack plate scooping water like a large spoon. This happens about 50% of the time when two are in the boat.
Fix: I've designed a skid plate for him to solve several of the problems with his jack plate assembly (mainly the scooping) and to also provide an additional running surface for planing purposes only.
Results: Hole shot with two aboard and full tournament load reduced from 6 1/2 seconds to 4 1/2 seconds with strong acceleration from the start. The rear has no chance of being locked down as before due to the scooping effect of the jack plate (see pics). Very little bow rise. Driver has visibility the entire time. No change in high speed performance as the plate is entirely out of the water at this point. Backwash is significantly reduced. This should enable him to try props for top end performance that never got him out of the hole in the past, i.e. 27" Trophy and/or Fury and should have a huge improvement on his fuel efficiency due to less strain off the start and the taller pitch of the prop.

Normal running position (BEFORE). Look at how easily water will scoop up and into the jack plate area on hole shot. He had water going over his motor cowling on every hole shot.


Normal running position (AFTER). The plate extends the set back surface and puts about a 7 degree hook at this location to lift the rear. It also ensures that water won't run up into the plate creating the huge scooping effect which is the most detrimental aspect of his poor hole shot.


Plate fully down (BEFORE). This is what made the plate design very difficult. See how the ram travels a good ways down.


Normal running position from underneath (AFTER). What is also accounted for in the plate design is that the ram can travel down through the plate without colliding with it. There is a .200" clearance built in.


Zoomed out view (BEFORE). Large cavities in the sides of the plate allow water to enter here as well. Not as severe of an issue, but still not desireable.


Zoomed out view (AFTER). Cavities are covered by side plates. Installation requires no modification to the current jack plate.



Mark
Re: Performance Results - Skid Plate Installation = 30% Hole Shot Improvement [Re: mcdil] #4410022 01/27/10 05:50 AM
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stick steering Offline
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i built my own 10 years ago mine is on a manual 10 inch t&h, my outside edges turn down a little more, it does help a little on holeshot and also helps pop the backend up at shut down cutting down on some of the backwash, i always heard them refered to as drag plates by some of the old racers, ive never had a adverse problem with mine

Last edited by stick steering; 01/27/10 05:51 AM.
Re: Performance Results - Skid Plate Installation = 30% Hole Shot Improvement [Re: stick steering] #4410424 01/27/10 02:24 PM
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East Bay Guide Jeff Brandon Offline
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Nice Work... my Bob's Hydraulic Plate has one of those on the bottom as well.


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Re: Performance Results - Skid Plate Installation = 30% Hole Shot Improvement [Re: East Bay Guide Jeff Brandon] #4424876 01/30/10 04:11 PM
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mcdil Offline OP
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Thanks, guys. Yeah, the Bob's has one from the factory that is the same size as the bottom area. When Gambler switched to their plate and provided the trim tabs at the same time, they attributed the much better hole shot solely to the tabs. Yes, they make a huge difference, but what was missed was the streamlined difference between the 12" Bob's plate and the 6" Detwiler with 4" setback that scooped water.


Mark
Re: Performance Results - Skid Plate Installation = 30% Hole Shot Improvement [Re: mcdil] #4424964 01/30/10 04:37 PM
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Nice work. I found similar improvements with a plate that covered the bottom of my 15" Rapidjack. Much better hole shot and lots less water over the back when shutting down.

I'm going to add some flotation (kid play balls) to the jack plate now that I have a top plate as well - I understand I may gain a bit more hole shot that way too.


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Re: Performance Results - Skid Plate Installation = 30% Hole Shot Improvement [Re: mcdil] #4434782 02/02/10 09:09 AM
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your skid plate has seamed to help his problem.What I want to know is #1. why didnt the owner just get a Bobs 10inch set-back power lift, one complete unit, no stacking,more rigid,no flex.#2 couldnt you reverse set back and jack places, have the jack against the boat and lift set-back and motor as one unit? Just wondering.


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Re: Performance Results - Skid Plate Installation = 30% Hole Shot Improvement [Re: Performance Outboards] #4434856 02/02/10 12:09 PM
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reversing would increase the leverage and put more strain on the unit, and bolting togehther essentialy makes it one unit, ive seen a six hydro bolted to a 12 manual before

Re: Performance Results - Skid Plate Installation = 30% Hole Shot Improvement [Re: stick steering] #4434867 02/02/10 12:25 PM
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mcdil Offline OP
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What you see in the pictures was the standard provided by Gambler in those years. He has not added anything back there. Going to a Bob's would be okay if he wanted to fork over a lot of money. Even then, the Bob's bottom skid plate isn't near the size of this one. Furthermore, the plates cannot be switched for the reasons mentioned above. Nor would it help. The set back plates would grab water as well.


Mark
Re: Performance Results - Skid Plate Installation = 30% Hole Shot Improvement [Re: mcdil] #4436713 02/02/10 09:26 PM
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steve@S2Marine Offline
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you should try a worked 26p bravo I for a kick tail holeshot!!!

another good prop is a txp 4 blade o/t4. when worked that gambler will come to life!

i know lot's of guys with gamblers with holeshot problems, and a worked bravo I has fixed them all.


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Re: Performance Results - Skid Plate Installation = 30% Hole Shot Improvement [Re: steve@S2Marine] #4439063 02/03/10 01:04 PM
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mcdil Offline OP
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Hey Steve,
A couple months ago, it was mentioned to him from Mark on the BBC to do just that. However, I told him to wait until we get this plate on. His problem was so severe, that he needed to fix it first. I've been trying to get him to let me design him a plate for it before he even bought the boat several years ago. I'm glad he finally listened. I'm the one who test drove the boat for him prior to buying it, and it used to be here in the DFW area at the time. It was the first thing I noted as an issuem but a fixable one.

He's gone through so much prop testing over the years in utter frustration. Not even a 24" Fury would come out of the hole without the passenger walking up front. I'm guessing this is due to the smaller disc size on the Fury versus the Tempest, where the Tempest will pick the rear up sooner alleviating some of the scooping. I realize the Bravo would have lifted the rear even more than the Tempest possibly solving the problem, but it's still inefficient and leaves him no room for prop experimentation. Not to mention coming off plane would still be a problem. He swamped the rear deck every time, even when feathering it. Ultimately, I think he would need a 28" Bravo anyway, and I know he would have had no chance coming out of the hole with it before. Top end speed is right around 82-83 for a short sprint with a 26" Fury he experiemented with some time ago with a light load and only him in the boat. This motor's a monster with the Brucato injection, and I think he could beat that with a little fine tuning.

The good thing now is the boat points forward allowing the water speed to lift the hull progressively while the motor continues to accelerate the boat forward allowing rpms to continue to build. It's very smooth and positive. Within reason, almost any prop is now an option to try, and he doesn't have to worry about going over on rpms at the upper end anymore with the tight pitch. I'll have to tell him about the TXP you mentioned above. I know he's considering a 27" Fury or Trophy. I think the 28" Bravo is still on the table as well. Thanks.


Mark
Re: Performance Results - Skid Plate Installation = 30% Hole Shot Improvement [Re: mcdil] #4439278 02/03/10 02:18 PM
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something else we used to do on gamblers and bullets. i'm sure alot of guys still do it.
stuff a car innertube or basket ball into the jackplate and air it up. that allows the back of the boat to sit higher while at rest. that helps the holeshot and doesn't allow the rear to get swamped when shutting down.

you're skid plate is cool too. i have built many of them years ago for guys.


www.hydrodynamics-usa.com
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