# Need input on LT25, Merc 25 2-smoke and JP setups



## TomFL (Oct 2, 2007)

I am going to hang the 25 merc 2-stroke on the back of the LT and need some help. 

I still have that manual JP that I won at the rally and am wondering if it'd be worth it to mount it on there and get a 4-blade prop. 

What are the downsides to running a 4-blade besides speed loss? How much speed will I actually lose? I think I was getting about 32 with noJP and the AL 3-blade and no JP last time I had this motor on the transom. 

Also, *HONESTLY* how much difference will this make in my running draft WITHOUT getting too extreme (as in, risking blowing up my motor from lack of water, etc). 

I'm just talking "set it and leave it" kinda stuff as it's a manual JP and I'm not going to be screwing with it every time... 

Thanks

-T


----------



## Brett (Jul 16, 2008)

Outboard mounted on transom











Outboard mounted on jackplate










Is that clear enough?  




> Boat Propeller Advantages/Disadvantages
> 
> Aluminum Boat Propellers: Advantage- cost. Disadvantage- blade flex and poor durability.
> 3 blade propeller vs. 4 blade aluminum propeller:
> ...


http://www.marineprop.com/propinfo.htm


----------



## TomFL (Oct 2, 2007)

About an inch!?!!??!?!

Brett, how dare you post a drawing without a scale representation as well as a super-imposed ruler!!!!! ;D

-T


----------



## Brett (Jul 16, 2008)

No scale for a good reason... ;D
Is the motor a long shaft? or a short shaft? or an extra long?
How much setback is involved?
Which brand outboard?
Brand determines the distance from the cav plate to the top of the water inlet.
But all in all, only a few inches difference, unless a tunnel is involved.


----------



## MATT (Apr 30, 2007)

Tom I run three blade with the Bob's plate set and get just over 30 per GPS Keep in mind I have a lot more weight in my LT then you will ever have.


----------



## Brett (Jul 16, 2008)

You run her tucked in Matt?


----------



## MATT (Apr 30, 2007)

Depends on how big the waves are that day. I have a lot of weight up frount. Gas, Trolling motor, Larges casting plat form etc....


----------



## Brett (Jul 16, 2008)

Yeah, with the 'fin and the down thrust that'd get the boat on plane quick.
and keep her on plane at lower rpms. I've been seeing a lot of 'noes configured that way.


----------



## MATT (Apr 30, 2007)

It's all about how the weight is spread out and keeping the nose above the waves.


----------



## TomFL (Oct 2, 2007)

Matt, it looks like you're running with the CAV plate a whole lot higher above the bottom of the hull than that ruler pic would lead one to believe. 

Any idea how much higher your cav plate is above the bottom of the hull?


----------



## MATT (Apr 30, 2007)

With the set back the fixed jack plate gives. You can run with the cave plate 3" to 4" above the bottom. That is the main reson for having the jackplate.


----------



## Brett (Jul 16, 2008)

Gent's, you're assuming that a boat in the water sits at the same angle as it does on a trailer.
Boats run bow high, usually 5 degrees.
That 5 degree tilt drops that cav plate way lower in relation to the bottom of the transom
than when it sits level on the trailer, look at them pics again Tom.


Bow high... 









think about that rotation of 5 degrees.


----------



## MATT (Apr 30, 2007)

It still means if you run a JP you can run with the cav plate above the bottom of your skiff. Play any number or degree game you need to. But do not use a flat 5% differnt hull shapes will make that change...


----------



## Brett (Jul 16, 2008)

I think that's what I tried to show in the first pics... ;D


----------



## TomFL (Oct 2, 2007)

What if I just raise the tongue of my trailer, will that help me run shallower??!?!??!     ;D ;D ;D

In all seriousness, yeah I agree we're not running with the boat level. But comparing apples to apples, Matt is running significantly higher than I am without the JP. Lots higher!

Matt, any issues with losing the water stream?

And running the 3-blade that high, no issues losing the grip?

-T


----------



## MATT (Apr 30, 2007)

None it has been running good for me.
you should bring your boat to Vero for the day..
"What if I just raise the tongue of my trailer, will that help me run shallower" this is the ******* way to add cup to your prop......


----------



## tom_in_orl (Dec 9, 2006)

Hey Tom, 

Here is my opinion. Its based upon experimentation with a Gheenoe Classic, Yamaha 30 HP 2 stroke, jack plate, and  a 3 blade prop. Its also based upon the more extreme Custom Gheenoe LT25, Yamaha 25 2 stroke, jack plate, tabs and 4 blade prop. 

Here is the Classic with 2" of set back. Manual jack plate raised 3 1/2". Besides the shallower draft it also ran  2-3 MPH faster. I honestly don't think that a 4 blade prop is much benefit on a fixed jack plate. I would stick with a 3 blade with mild cupping.





































The LT 25 is not much different. IMHO, you can do a lot with the right equipment. I am able to raise my motor 11" (not a typo). To do that you have to start with an adjustable electric or hydraulic jack plate, then add a 4 blade prop and tabs. (I will take some pictures of motor fully raised up tomorrow.)

So bottom line. My recommendation for a manual jack plate with 2 - 4 inches of set back is to stick with 3 blades and mild cupping. Start by raising your motor 3".


----------



## redgheenoe (Apr 28, 2007)

Get an airboat!


----------



## tom_in_orl (Dec 9, 2006)

Airboats aren't allowed in Mosquito Lagoon.


----------



## Tom_C (Dec 10, 2006)

There are so many factors 

A Lt Transom is 20" if it notched for a 15" motor the notch will be 18.5"

Matt from just looking at your pictures, your jack plate is set at 20.5"" with a 7" setback (6" jack plate + 1" mounting block). You also have a Cav Plate attachment and a SS Prop. Your motor has around a 16.5 shaft. Each of these add to factors that are in play. 


Tom's Classic has a 17" transom with a motor shaft of about 16.5", so with the jack plate at 3.5"  his motor is at 20.5". 

So in my opinion both of these motor are even with each other, but because Tom only has 2" setback his is more extreme. 

Now for Tom's LT, his transom is 20" he has a 20 motor that has about a 21.5" shaft. So he started with his motor 2" lower that a 15" motor on a Classic. Tom correct me if I am wrong. Your boat has a 5" raiser, a Jack Plate with 6" setback and 6" travel. With your Jack Plate down your motor height is 25". So your Cav Plate height would be 1/2 lower than  Matt"s Cav plate. A 20 motor on a 25" transom / a 15" motor on a 20.5" transom. 

Plus Tom has a 4 blade SS prop (with cupping?) and Ele Trim Tabs. Again each of these add to factors that are in play.

Matt can you take a pic that show relationship between the top of the transom notch and your motor thumb screws? My guest is your motor thumb screws are just below or even this the top of the notch. The reason for my request is to see if you had a 4” setback jack plate would the thumb screw hit the top of the transom?


----------



## backwaterbandits (Dec 15, 2006)

Tom, when I first got my LT 25 w/the Bob's manual
   JP I had to run my Yami 25 2stk all the way down 
   with the stock prop or it would blow out badly. 
   (Even with me in the back)
   I installed a Bob's Tru-Tracker and a 4 blade SS prop
   with Skiff Shop cup and now run the JP all the way
   up.
   As far as speed, I get about 25-26 fully loaded w/2
   people and all gear and Lin-X on the whole hull...
   Dave


----------



## noeettica (Sep 23, 2007)

I think that's Up ;-) Mr. Dave :


----------



## TomFL (Oct 2, 2007)

> Tom, when I first got my LT 25 w/the Bob's manual
> JP I had to run my Yami 25 2stk all the way down
> with the stock prop or it would blow out badly.
> (Even with me in the back)
> ...


This is precisely what I'm wondering.... Is it worth it with this JP, really no setback, and an AL 3-blade. I really don't have the budget to go through the whole deal of a custom SS prop, tabs, etc on this hull. 

I'm looking to just "set it and forget it" and if I can run 2-3" shallower, not kill the boat in the turns, still get up on plane easily, and not blow up my motor from lack of water, that'd be perfect. 

If I can't do that without adding more setback, a custom 4-blade, tabs, etc., then it's not worth it to me. 

-T


----------



## Flyline (Mar 3, 2008)

If I were you, I will do what Tom-in-Orl recommends....get a manual jackplate 2-4" set-back (set it up and forget it) and 3 blade S.S prop with mild cupping.

Reason why with mild cupping is less slippage on the prop and bites the water better.

It will help u to run bit faster and shallower.

I had a classic and LT25 with electric jackplate, stabilizer plate and 4 blade propeller worth around $1500.00 just run 5-7" shallower......I like it.

But is it worth it to spend $1500-2000 just for electric or hydraulic JP, 4 blade propeller with heavy cupped and tabs to run in 6"-8" of water?? I don't know.


----------



## TomFL (Oct 2, 2007)

> If I were you, I will do what Tom-in-Orl recommends....get a manual jackplate 2-4" set-back (set it up and forget it) and 3 blade S.S prop with mild cupping.
> 
> Reason why with mild cupping is less slippage on the prop and bites the water better.
> 
> ...


Not when the tunnel hull will run in 5"!!

Just looking to utilize the JP since I've got it. But if it's not going to add any benefit without adding a bunch of costly new items, I might be better off without it!

-T


----------



## Brett (Jul 16, 2008)

How high could you mount it now, without adding any extras?
Just using the clamps as is, or through bolting the transom?


----------



## TomFL (Oct 2, 2007)

> How high could you mount it now, without adding any extras?
> Just using the clamps as is, or through bolting the transom?


If not mounting the JP, then just using the bolts in the holes that are there in the transom from when CaptnRon had it. 

Pic ain't really worth a darn for this purpose, but it's the only pic I had









-T


----------



## MATT (Apr 30, 2007)

Tom, just bring the LT and JP to my place and we can set it up. You already have the JP and it is a good product if only to add the set back that wil add more water flow over the lower end. This is what lets you rase the motor. Call me...


----------



## Yoreese (Oct 15, 2009)

I am looking at purchasing a new LT25 and have a 25 Merc 2 stroke/elec. with Merc Stainless prop. I am being told to run the motor on the transom. It sure looks like the set-back jack plate would be the ticket.


----------



## TomFL (Oct 2, 2007)

> I am looking at purchasing a new LT25 and have a 25 Merc 2 stroke/elec. with Merc Stainless prop.  I am being told to run the motor on the transom.  It sure looks like the set-back jack plate would be the ticket.


Honestly if the boat didn't run that good without the JP, I wouldn't really be considering putting it on there; I'd have done it already. 

I think you'll find your setup will be super-sweet, JP or no JP

-T


----------

