Pitch change to help heavy load

Joined
Feb 19, 2006
Messages
14
Hi Guys, I have a Carolina Skiff with a 15 hp Honda 4-stroke. My problem is when I take my wife and a cooler,my motor won't get up the rpms to get to plane. It sounds terrible. When I'm alone and empty out the boat,it's much better.I own 2 props, a 9 1/4x 9, and a 9 1/2x 8 5/8.It does run a little better with the 8 5/8 pitch. I do not have a tach.I know I probably need a 20 hp, but that's not gonna happen. They make a 9 1/4 x 8, and a 9 3/4 x 6 1/2. What would I expect for change with each of these props ? I really don't want to buy a tach.
 

WillyBWright

Fleet Admiral
Joined
Dec 29, 2003
Messages
8,200
Re: Pitch change to help heavy load

The 6-1/2 is a pontoon prop. The 8 sounds worth looking into.
 
Joined
Feb 19, 2006
Messages
14
Re: Pitch change to help heavy load

So, the 6 1/2 pitch would make what change. Would it allow more rpms and therefore allow more top speed. I am confused.<br /> I just found 2 other props... 9 1/4 x 8 and a 4 blade 9 1/4 x 7....Which one do you think ??
 

Texasmark

Supreme Mariner
Joined
Dec 20, 2005
Messages
14,721
Re: Pitch change to help heavy load

It sounds terrible because you are probably lugging the heck out of it. The difference between your two props is insiginficant (diminsions) but it seems you are getting a noticeable performance change (enough to notice, not noticeable like a lot).<br /><br />Hard to second guess your situation. No doubt you need to drop your pitch, but will 8 do it or 7, only running the prop will tell you for sure.<br /><br />If you go with the 7, you may not get on plane.<br /><br />I just ran some hypothetical numbers thru the prop calculator and it looks like the 8 would do you the best if it allows your engine rpm's to come up where they belong. The 7 wouldn't get you on plane.....13 mph. <br /><br />So for a SWAG, (and that's all it is till you try it) I would go with the 8P.<br /><br />The good thing about a Carolina is that they have a good flat hull that will plane out easily.<br /><br />The other thing you want to insure is that you distribute your load so that you maximize your speed. You can easily tell by moving people and things around till you get the best performance.<br /><br />Moving the engine our or in (via the tilt pin) needs to be investigated also again for best performance.<br /><br />HTH,<br /><br />Mark
 
Joined
Feb 19, 2006
Messages
14
Re: Pitch change to help heavy load

Thanks for the info Mark. Should I get the 9 1/4 x 8 in a 3 blade or 4 blade. They make both. If they both got the boat on plane, which of the 2 would pull a heavier load. Also,do you know which would go faster.By the way, the performance change[getting on plane] happens when I lighten the load. Thanks, Pete<br />p.s. I posted this on another forum, but I'll try you guys on it...What would the proper wot rpms be for this motor. My manual says 6200, Hondas website says 5500. It's a 1999 BF 15
 

studlymandingo

Commander
Joined
Mar 22, 2006
Messages
2,716
Re: Pitch change to help heavy load

The 4 blade will be more responsive to the heavier load, the three blade will most likely make you go faster. A 50HP will solve all your problems!
 

Texasmark

Supreme Mariner
Joined
Dec 20, 2005
Messages
14,721
Re: Pitch change to help heavy load

10-4 on the higher hp. You are pushing the envelope on the low end. Agree with Studly, get more hp.<br /><br />On 3 or 4 blade where you are, I have no idea.<br /><br />Mark
 
Joined
Feb 19, 2006
Messages
14
Re: Pitch change to help heavy load

I hear you about the HP. The boat is a J-14 and is only rated for a 20. I am also in the Bahamas and to try to sell this 15 and get a 20 would be like bying and selling a house in the states.The other thing is we're close. If I remove some weight it runs great. I don't think this setup is beyond the relm of possible. Now that I found I can run 6200 rpms, I think [I HOPE] that 7P 4 blade will do it.I'll let you know.It'll take a week to get the prop here.
 

studlymandingo

Commander
Joined
Mar 22, 2006
Messages
2,716
Re: Pitch change to help heavy load

Bahamas...mmmm which island? Let's see, I can trailer to Ft Lauderdale in 3 hours, Bimini is a 2 hour ride from there... How much is shipping??? Let me check with the IRS, maybe this is how to write off a fishing trip!!! :D ;)
 
Joined
Feb 19, 2006
Messages
14
Re: Pitch change to help heavy load

I'm on Cat Island. Shipping and Duty for the boat cost more than the boat !!! Shipping for the prop will be a $1 per pound, via Lynx air. Trust me, the IRS is not welcome here ....Bye the way, how much speed do you think the 4 blade will lose over the 3 blade same pitch..
 

studlymandingo

Commander
Joined
Mar 22, 2006
Messages
2,716
Re: Pitch change to help heavy load

On that motor, not much to notice, sounds like you need the holeshot more than anything else. I think the 4 blade may be the way to go.
 

solidwaste

Petty Officer 2nd Class
Joined
Jul 12, 2005
Messages
106
Re: Pitch change to help heavy load

Id look into buying one of the SAIL motors if I were you those chinese knock offs there pretty cheap so when you get done with purchase and duty and taxes youll only have to pay $4000.00 for a $1800.00 motor..
 

Texasmark

Supreme Mariner
Joined
Dec 20, 2005
Messages
14,721
Re: Pitch change to help heavy load

I wouldn't spend money on a 20 if you have a 15. On the 3 or 4 blade, the 4 blades were made for bassboats with fat asses that needed to get out of the water. Well, with your Carolina, it's not necesarily a fat ***, but with only 15hp it may act like one.<br /><br />Additionally, the 4 is said to reduce vibrations; but according to Merc, it's less efficient....probably due to turbulence. So all this stuff is just smoke.<br /><br />What's important is what you have and how you use it and the results you get.....the rest is just conjecture......sorry, but that's the way it is.<br /><br />Good luck....but the numbers says that a 7 is too small.<br /><br />Mark
 
Joined
Feb 19, 2006
Messages
14
Re: Pitch change to help heavy load

Hi Mark,<br />What type of calculator do you use? I also wonder,could you tell me how do you determine a particular boats planing speed? The calculator that I found online says if the motor turns at 6200 with a 7p and 15 % effiency loss, the boat will go almost 16 mph. Is that enough to plane ?Also, what do you think if I went with 3 blade and ventilated it. I did that to a bass boat that I have and shot out of the hole . I just don't think going from a 8 5/8 to an 8 will do much for me.I wish they made a 7 1/2.Also, could smart tabs help my problem ? I wonder, maybee if I lost the extra 50 lbs. that I recently found, it would solve all of my problems.
 

Texasmark

Supreme Mariner
Joined
Dec 20, 2005
Messages
14,721
Re: Pitch change to help heavy load

I use a BAM of Florida calculator....www.gofast.com. Have found that it work real well for what I need and do. May be off for other applications (heavy, as I am light) but it works. Big variable is prop slip and the more you are dragging your *** the more slip you encounter.<br /><br />Planing speed depends on the hull design and weight. A really light john, with a lot of flat bottom may plane at 10 mph. A heavy deep V may have to get to 20 before the water vee leaves the transom.<br /><br />Lot of question. Check my reply to your last post. Best I can do.<br /><br />Good Luck,<br /><br />Mark<br /><br />Mark
 
Joined
Feb 19, 2006
Messages
14
Re: Pitch change to help heavy load

I just had to tell you guys, after dicking around for 2 years, buying 4 props, moving the motor hieght, tuning it up, waxing the bottom, and rigging a sail, I finally just bought a brand new Honda 40 hp...!!!!!!!!!!!! I'll be shipping it down this nov. 1 and I'll let you know how it flies. Any recomendations on a prop for this rocket?
 
Top