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performance enhancement (maxing out hp)


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#1 sauce

 
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Posted 16 July 2017 - 04:21 PM

I recently bought a 16 foot princecraft. It came with a 25hp Johnson 2 stroke tiller. The boat weighs 575lbs according to the princecraft catalog. Add batteries gear etc and it's probably close to 750lbs. Add myself and a passenger, now well over 1000lbs.

It actually scoots along pretty good. Getting up around 25mph on the GPS. Hole shot is not great. And in order to get up on plane quick, I need to have weight in the bow (fill the livewell or get buddy to sit up front)
The boat is rated for a 40. So I'm at 62.5% of rated maximum.
A 30 would put me at 75% and if I could find a 35 I would be at 87.5%
So, my questions...
Will I notice a big difference going up to a 30? Or am I better off to be looking for a 35 or 40?
Thanks for any input you can offer. I'm very happy with my new rig. Not looking to be the fastest 16 footer on the water, just looking to boost performance a little.

#2 67ZL1

 
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Posted 16 July 2017 - 06:03 PM

I have a Lund SSV-16 with a 40 Merc 4-stroke. Loaded with gear, 2 batteries, drop in flooring, 3 adults and a 110 pound Labrador it will run at 34-36 mph on GPS. That is with a 13P Spitfire 4 blade prop.

Edited by 67ZL1, 16 July 2017 - 06:04 PM.


#3 porkpie

 
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Posted 16 July 2017 - 06:10 PM

I doubt 5hp will show you exceptional increase. If you want to get up go, and your set on upgrading your motor, I'd look for the 40.

#4 Sinker

 
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Posted 16 July 2017 - 06:55 PM

Get the 40.

#5 Old Ironmaker

 
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Posted 16 July 2017 - 07:03 PM

Post this on iboats.com. They know there stuff, we do too but they are some super guys there and it's 100% boating on the general boat forum. I have come to learn that the difference from a 9.9 and a 15 horse is simply a different carburetor. Same goes for a 4 stroke 250 horse Merc to a 300 HP Merc, fuel delivery is maxed on the same engine. There are kits to upgrade HP but you need a 40. I strongly believe you won't see any difference with a 5 HP upgrade.

If you want maximum power and speed go with the maximum HP rating for the boat.

#6 Tupelo

 
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Posted 16 July 2017 - 07:09 PM

Before you go that route, have you checked to see if your Prop is the correct size?  Maybe a 4 blade would help - from what I understand it drops the top end speed, but makes the hole shot/handling better.   I will probably go that route myself, and keep my current 3 blade as the backup.

 

Anyway - might want to check that first, as it is much cheaper than a new motor - lol.



#7 dave524

 
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Posted 16 July 2017 - 07:13 PM

5 hp won't show much increase, especially if you go from a 2 stroke to a 4 stroke.



#8 OhioFisherman

 
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Posted 16 July 2017 - 07:37 PM

If you're going to upgrade your horsepower? Make it a one time deal and get the 40.



#9 Woodsman

 
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Posted 16 July 2017 - 07:58 PM

A further on Tupelo's post.

First make sure you have the correct prop that is maximum for the set up of your boat as you normally use it.

The best way to do this is by running your boat wide open on flat water and checking the RPM.

Next compare this to the maximum rated RPM for your motor.

Is the RPM within the maximum WOT range recommended by the manufacturer?

If yes than you need more motor for better performance.

If no you can improve the performance by changing props.

If the difference is minor than the improvement will also be somewhat minor.

But if your boats RPM at WOT is far out of the maximum range than the improvements can be very noticeable.

Sometimes there is no replacement for HP though.


Edited by Woodsman, 16 July 2017 - 08:00 PM.


#10 KLINKER

 
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Posted 16 July 2017 - 07:58 PM

You might try a whale tail.

#11 Mike Rousseau

 
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Posted 16 July 2017 - 08:01 PM

When I went from 40hp to 50hp I noticed I had more power when fully loaded

#12 Pigeontroller

 
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Posted 16 July 2017 - 08:06 PM

Max it out.



#13 Spooled

 
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Posted 16 July 2017 - 08:20 PM

If you've already optimized the prop and motor height in the 25 and need more, than I'd look at the 40s and find one that is light. Different brands can vary a lot for weight of actual motors.

#14 sauce

 
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Posted 16 July 2017 - 08:31 PM

Thanks for the input. I'm running a 4 blade aluminum prop. I have no idea what rpm I'm running at though. I don't like the whale tail idea. For now I will be sticking with the 25. And when I do upgrade I will most likely be looking at 35 and 40 2 strokes. Problem I'm running into is that I don't see a whole lot available in the used market.

#15 GBW

 
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Posted 16 July 2017 - 08:49 PM

Problem I'm running into is that I don't see a whole lot available in the used market.

You may not see them but they are out there.  

What I mean is place an ad posting what you want and that may provoke someone with a 35 or 40 wanting to jump to a bigger unit as well for their boat to reply and make you an offer.  Ad's are free so no harm there right?  

Good luck and yeah MAX it out like the others have said.  



#16 GBW

 
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Posted 16 July 2017 - 08:51 PM

FYI I just seen this in the short time since my last post

http://www.kijiji.ca...gationFlag=true



#17 GBW

 
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Posted 16 July 2017 - 08:52 PM

this is the whole list in my area that has a 40HP for sale (some full boat pkg's) 

http://www.kijiji.ca...p/k0c29l1700218



#18 Old Ironmaker

 
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Posted 16 July 2017 - 09:05 PM

There are plenty out there. When I get back on my feet I'll look around at my little buddy's building for one.

#19 sauce

 
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Posted 16 July 2017 - 09:18 PM

I appreciate the help guys. At the present time I'm not in the market to buy. Just giving it some thought. I'm actually a little surprised at the performance of the 25 on this boat. I would say it's almost enough power. It takes a little to get up on plane but it definitely goes once the bow comes back down!

#20 Old Ironmaker

 
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Posted 16 July 2017 - 09:31 PM

Whale tail may help get on plane faster. Why the aversion to one? Prop match is important but won't get you 60% more power on a 25HP. Only a 40 will do that.





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