Prop'd out? (need for speed)

[Hopsdak]

Howdy fellas,<br />I've got a few questions about my current setup.<br />I have a 18' gulf coast with a Johnson 130 on it. <br />It looks alot like a boston whaler. It has a displacement of 1,200#'s and prolly another 400 or so with gear and persons aboard.<br />Port Side Picture, Stern Picture, and Stern 2 Picture <br /><br />My question is how fast should this boat run?<br />I've reached a max speed of 40mph @6,100 rpm.<br />The prop that is currently on there is a 13-3/4x16 as far as I can tell. I know it's a 16 because that is stamped on it. The dia I had to use a tape on. It's a four bladed and is stainless. The hole shot is enough to pitch a person out of the boat if they aren't holding on. <br />Would going to a 3 blade 18 pitch give me any more top end? The boat also has a jack plate to help tweak out the trim. I'm looking for a good spare prop that I can use on days when the bay is flat and I can put the hammer down. Any help would be appreciated. <br />Thanks, Hop<br /><br />P.S. I forgot to add, What props are interchangeable on this outboard? Will a prop off a 115 or 250 fit? I used a tape to pull a dimension from the shaft to the cav plate and i measured 9" so anything under a 17" dia should fit right?

 

[quantumleap]

Re: Prop'd out? (need for speed)

I'm assuming your jackplate is raised for towing and you dont run your motor quite that high. Going to the 18 pitch should raise your top speed as your RPM's are pretty high with the 16. What is the recommended rpm range for your 130? Good looking boat!

 

[Hopsdak]

Re: Prop'd out? (need for speed)

The motor is a J130PLSS, And I think the optimum rpm range is 5k-6k. Your correct about the jack plate. It will run with it that high up because of the tunnel but, it tends to cavitate if I have to turn. I usually run it just under the point of cavitation (adjusting the trim and jack on the edge of blowout) leaving nothing but prop in the water. That's only when it's smooth. Thanks for the complement!

 

[Hopsdak]

Re: Prop'd out? (need for speed)

I'm wondering if maybe i should have posted this under general outboard ...

 

[Jdeagro]

Re: Prop'd out? (need for speed)

The boat should do 45mph, and all of the extra lifting devises are holding you back. They are lifting the stern and pushing the bow down, then you trim the motor out to lift the bow to compensate. Now the prop is running through the water at an angle trying to propell the boat and lift the bow. Props are for propelling and when used to do other things you compromise the performance. Both the hydrofoil and the Step and Trim plate (fixed Plates) are providing too much lift at high speeds. No question in my mind!<br /><br />If you wish call me at 800-233-0194 and I will mail you a technical paper on boat balance and performance which will explain this in graphics and text.<br /><br />Don't bother changing the prop until you get the hull back to what it should be. I do think you will benefit from trim tabs but they can not be rigid or fixed. The boat will be faster if you remove the plates and the foil, it won't plane easily but it will go faster. Call!<br /><br />John

 

[Solittle]

Re: Prop'd out? (need for speed)

I think the max rpm for your motor is 5,5-5,800 rpm though 6,100 should not hurt it. I would think a 3 blade 17" will give you more top end, drop the rpm a couple of hundred and not effect the hole shot an awful lot. Try to find a prop shop who will work with you - try before you buy.

 

[MajBach]

Re: Prop'd out? (need for speed)

I have a friend with a very similiar boat - Wahoo 18'. He has a Merc 115 2-stroke with a regular 3 blade aluminum. His hole shot is not the best but top end is approaching 50 mph. Your hull looks like a faster one than his too. Apples to oranges?

 

[Hopsdak]

Re: Prop'd out? (need for speed)

nautiJohn,<br />Getting the hull back to square one is not an option. The trim tabs are in the full upright position (1/2"-1" A.B.L.).And the foil is out of the water when I run the jack up. All that is in the water is the prop and it's being fed by the tunnel. Like I said when I turn with it in that position it will cavitate. I know it's providing some lift but, to compensate for not having the foil I have to run the motor almost all the way down on the jack to keep it from cavitating. Thus creating more drag from the lower unit. <br /><br />SoLittle, I'll try finding a shop locally. I'm thinking of getting another 4 blade but, in a 18 or 21 pitch with the same or close dia.<br /><br />MajBach, You wouldn't happen to know what pitch your friend is running do you?<br />I assume this is the same style hull he's running..<br /> http://www.dachshundpups.com/boatsforsale.html <br /><br />Thanks, Hop

 

[phatmanmike]

Re: Prop'd out? (need for speed)

lower your motor a inch or so next time, and get a 3 blade 17 ptch or even 19 depending on how light your boat is... your rpm is way high, get it down to 55-57 hundred and youll see a big improvement

 

[Hopsdak]

Re: Prop'd out? (need for speed)

Originally posted by phatmanmike, again:<br />lower your motor a inch or so next time, and get a 3 blade 17 ptch or even 19 depending on how light your boat is... your rpm is way high, get it down to 55-57 hundred and youll see a big improvement

I usually run with my motor down a ways until i plane out. Then once i'm on plane i jack the motor up and trim it out until i reach the max speed and rpm i can without blow out. I'm still thinking that maybe i need a 4 blade and just up the pitch a bit. I'm not sure if it will take off with a 3 blade w/o cavitating.<br />Ah well, Thanks for the replies, I'll let y'all know what i come up with. <br />later, Hop<br />(off to find a prop shop)