# boat prop question



## TightLines172 (May 13, 2011)

Hey guys I have a 2000 sea hunt triton 172 with a Nissan ns90a 2 stroke. Its currently has a 13 1/4 x 17 aluminum prop on it. I also have a 13 1/2 x 15 prop that came with the boat when I bought it. This spare prop is brand new. I want something that will get me out of the hole quicker and have a higher top end speed. The other day my mother in law had a friends new mako 18 ft boat out and she had 4 people on it and I only had myself and one other person on mine. The mako has a new mercury 90 4 stroke on it with a ss 4 bladed prop. She kicked my butt when we raced. Is that just the difference in the 2 and 4 strokes? Any suggestions for a faster more "Torquey" prop? Thanks in advance!


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## TightLines172 (May 13, 2011)

Oh yeah, any idea what my spare prop will add/subtract from my motor's performance?


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## Mac1528 (Mar 24, 2012)

There are several formulas (guesstimates) on the internet you may want to look up. I know when I spec'ed mine out (90hp Honda 4 stroke) I wanted best fuel performance and decent top end. The rep told me that out of hole quick & top end speed are opposites. You either get one or the other. Also that add on tail to the cavation plate helps out of the hole a little. Happy hunting!


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## SHO-NUFF (May 30, 2011)

Get a stainless steel prop. An aluminum prop will flex. It makes a big difference on most boats with the same pitch and diameter props. 
You have to sacrifice top end for a good hole shot, or sacrifice the hole shot for more top end. The boat should be propped where it runs real close to the engine redline RPM's at wide open throttle.


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## Wad Shooter (Jul 31, 2012)

You will get out of the hole quicker with the spare. Your rpms may also increase with the spare. Higher pitch lowers the rpms because it makes the engine work harder. However in your case you will decrese the pitch and add more prop by 1/4 of an inch so you may not see much of an rpm increase. Strap it on and try it out. A jack plate can greatly increase top end. Less motor in the water creates less drag, but you've got to have enough water for the prop to bite. Youve got to find the sweet spot with a jack plate. 4 blade props are more for torque and hauling a load but not as effeciant when talking about top end because once again your creating more drag with 4 blades vs 3. Next time on the water bring a wrench and try them both out.


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## Wad Shooter (Jul 31, 2012)

SHO-NUFF said:


> Get a stainless steel prop. An aluminum prop will flex. It makes a big difference on most boats with the same pitch and diameter props.
> You have to sacrifice top end for a good hole shot, or sacrifice the hole shot for more top end. The boat should be propped where it runs real close to the engine redline RPM's at wide open throttle.


This is true in some cases but lower hp motors such as a 90 may not flex the prop enough to make a difference. If her were running a 150 or bigger stainless would make a difference as far as flex but a 90 won't flex much.


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## SHO-NUFF (May 30, 2011)

Just speaking from personal experience.

I am running a 115 Yamaha with a stainless 13x15 prop on a 19 foot Proline CC.
I have a brand new 13x15 aluminum prop for a spare and tried it out on the boat and it performed terrible compared to the stainless prop. Not so much as hole-shot but the top end fell way off. 

I think his boat might be over propped with the 17 pitch he is currently running and is not getting the max RPM's. It's hard to find many friends running nissian/tohatsu engines to borrow a test prop from also.


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## OLDBOB (Jan 27, 2013)

*Sea Hunt/90 Nissan prop issue*

I have the same boat and motor setup as you. Right now I have a 17" pitch SS prop that had been cupped and I took it to a prop shop and had some of the cup removed to get the rpm up. The problem I have is that I have to trim the motor way out to get the rpm and the speed up. I can get 5600rpm out of the motor this way, but with that much trim so much of the boat is out of the water that the steering control get squirrelly in choppy water. The speed is in the low 30s. ( at 4000 rpm I get 28 mph according to my GPS )With the motor trimmed in about half way it accelerates reasonably well, but I don't know how it would do in a race. If you live near Navarre, I would be willing to compare it.
I had an aluminum 15" pitch, stock Nissan prop, but I didn't see an increase in acceleration with it and it couldn't tow anything worth a darn.
I don't have trim tabs, but the fellow that owned the boat before me put on one of the hydrofoil things on the cavatation plate.
My motor runs very strong according to what I see, and the mechanics that have looked at it.


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## TightLines172 (May 13, 2011)

Thanks for all of the responses. I guess o need to try it out. With just me I have trimmed the motor out really high and topped out at 42 mph by gps in smooth water. With 2 people I average around 32 to 34 mph without a problem and my max rpm has only been about 5k. I can't get it any higher without the prob spinning out. I do have a hydrofoil fin on the cavatation plate too. So of I'm reading this correctly, I should have more torque out of the hole with my spare... any ideas on how much top end I'll loose?


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## TightLines172 (May 13, 2011)

OLDBOB said:


> I have the same boat and motor setup as you. Right now I have a 17" pitch SS prop that had been cupped and I took it to a prop shop and had some of the cup removed to get the rpm up. The problem I have is that I have to trim the motor way out to get the rpm and the speed up. I can get 5600rpm out of the motor this way, but with that much trim so much of the boat is out of the water that the steering control get squirrelly in choppy water. The speed is in the low 30s. ( at 4000 rpm I get 28 mph according to my GPS )With the motor trimmed in about half way it accelerates reasonably well, but I don't know how it would do in a race. If you live near Navarre, I would be willing to compare it.
> I had an aluminum 15" pitch, stock Nissan prop, but I didn't see an increase in acceleration with it and it couldn't tow anything worth a darn.
> I don't have trim tabs, but the fellow that owned the boat before me put on one of the hydrofoil things on the cavatation plate.
> My motor runs very strong according to what I see, and the mechanics that have looked at it.


I do live in Navarre and would like to compare sometime. Please shoot me a pm sometime.


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## CootCommander (Aug 24, 2008)

Mac1528 said:


> There are several formulas (guesstimates) on the internet you may want to look up. I know when I spec'ed mine out (90hp Honda 4 stroke) I wanted best fuel performance and decent top end. The rep told me that out of hole quick & top end speed are opposites. You either get one or the other. Also that add on tail to the cavation plate helps out of the hole a little. Happy hunting!


Not necessarily true. If your prop doesn't get you into your ideal operating rpms at WOT you will gain both hole shot and a higher top speed by reducing the pitch. Going from a 19 pitch to a 15 on my Yamaha F150 gave me 800 more rpms (200 per 1 degree of pitch) and 4 more mph on the top end. 

You want to be as close to your ideal WOT rpms as possible with your normal load.


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## sealark (Sep 27, 2007)

You are looking for the impossible. Just get the engine to it recommended RPMs with the max normal load and be happy. A stainless cupped prop will give you better performance. If the engine isn't at it's recommended RPMs you are either overloading the engine ( Max RPMs under rating). OR not getting the full power of the engine and wasting fuel ( Max RPMs over rating).:thumbup::thumbup:


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## DAWGONIT (Jan 16, 2009)

++ on proper RPMS @ WOT; generally 55/5600-6000 per manufacturer.


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## TightLines172 (May 13, 2011)

sealark said:


> You are looking for the impossible. Just get the engine to it recommended RPMs with the max normal load and be happy. A stainless cupped prop will give you better performance. If the engine isn't at it's recommended RPMs you are either overloading the engine ( Max RPMs under rating). OR not getting the full power of the engine and wasting fuel ( Max RPMs over rating).:thumbup::thumbup:


I don't think I'm asking the impossible here...I'm asking for advice. If the ideal rpms are around 5500, I'm not getting anywhere near that. If changing to the 15 pitch prop will increase my rpms then I will give that a shot. I'm not unhappy with my motor by any means, I have just had some difficulty at times getting out of the hole quickly.


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## TightLines172 (May 13, 2011)

Ok I swapped out the prop for the lower pitch. As soon as we get a break in the weather I'm gonna try it out and will post the results. Thank you EVERYONE for your well informed responses!


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## sealark (Sep 27, 2007)

Tightlines the impossible I stated was for your wanting more hole shot and more speed. You CANT get both, that's what's impossible you will give up one for the other...


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## TightLines172 (May 13, 2011)

sealark said:


> Tightlines the impossible I stated was for your wanting more hole shot and more speed. You CANT get both, that's what's impossible you will give up one for the other...


I gotcha. My hopes were since I'm not getting my rpms up as high as they should be, maybe I can get a little of both with the proper pitch...thanks for the info!


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## sealark (Sep 27, 2007)

Yes but in order to get the RPMs up you reduce the pitch. That means you will most likely reduce speed. There is also your slippage could be reduced with a lesser pitch and speed will stay close to the same but I doubt it will.


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## TightLines172 (May 13, 2011)

sealark said:


> Yes but in order to get the RPMs up you reduce the pitch. That means you will most likely reduce speed. There is also your slippage could be reduced with a lesser pitch and speed will stay close to the same but I doubt it will.


Thanks for the info! Will def give it a test run as soon as I get a chance! I wanted to go yesterday when we got a little break in the weather, but my wife had other plans...lol


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## TightLines172 (May 13, 2011)

Well I finally made it out on the water this evening for a test run with a nice looking storm in full view. All i have to say is wow at the difference! My hole shot improved from about 8 to 9 seconds normally to reach plane to about 3 flat and my rpms at WOT jumped from about 4800 max to 5600 max. My top speed with myself and a friend and an almost full tank of gas stayed right at 37 to 38 against the wind and against the current. Its perfect and it feels like I have a whole new boat. Its amazing the difference the right prop can make! Thanks for all the input and knowledge! See you out there...


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## SHO-NUFF (May 30, 2011)

Glad it worked out for you!
The max RPM's are exactly where they need to be now. You were over propped before, to much pitch. This is what makes this Forum work.


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## sealark (Sep 27, 2007)

Now that you got the engine RPMs correct is the engine high enough? when plaining at high speed is the lower cavitation plate out of the water? If it isn't just above the water level a slight bit you are loosing more economy and speed. Lastley keep that fuel tank topped off AFTER every trip (Prevents Condensation) and use or at least run the engine regulary. Water in the fuel is your worst enemey not ethenol fuel.


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## TightLines172 (May 13, 2011)

sealark said:


> Now that you got the engine RPMs correct is the engine high enough? when plaining at high speed is the lower cavitation plate out of the water? If it isn't just above the water level a slight bit you are loosing more economy and speed. Lastley keep that fuel tank topped off AFTER every trip (Prevents Condensation) and use or at least run the engine regulary. Water in the fuel is your worst enemey not ethenol fuel.


Yes, I have one of those fins on the cavitation plate and keep it just above the water level on plane. Works like a charm. I have a fuel/water separator on it so I don't usually top off the tank AFTER a trip, but that's good advice. So far having had any water in fuel problems...knock on wood...I also keep my boat under a carport so the heat change during the day is a little less than it would be if in direct sun.


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## TightLines172 (May 13, 2011)

Oh yeah and it gets used or at least run on a hose in the driveway every weekend...tends to run a little rough at startup if I let it sit too long


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## DAWGONIT (Jan 16, 2009)

glad it worked out & thanks for updating us.


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