Looking for Propellor suggestions?

[jhuds4]

Hey y'all, I've got a 24' fisher pontoon with a 2004 mercury 115hp 4 stroke. I believe it currently has a 3 blade, will top out at 5500 rpm, and will do about 21mph on the gps. I called Mercury and the guy said his best guess for a replacement would be a "spitfire" 4 blade with 15 pitch. Was looking to get some second opinions. Thanks!

 

[WesNewell]

Start here
https://www.mercurymarine.com/en/us/propellers/selector/#!/step-one

 

[roscoe]

Why are you looking to replace the prop?
Looks like it is about right to me.

 

[jhuds4]

Why are you looking to replace the prop?
Looks like it is about right to me.

The prop looks pretty banged up and the motor vibrates a lot making stuff on the boat rattle- just seems like something isn't right as the motor runs rough, thought the prop would be a good place to start.

What is typical pitch and size for a motor that size on a 24' pontoon? I'm leaning toward 3 blade 14'' 13 pitch

 

[Sea Rider]

Do you know what's the min-max wot rpm range for that 4 strokes 115 HP engine ?

Which pitch is the current installed 3 blade prop ?

How loaded do you like go boating, lightly, medium or heavily loaded ?

When achieved 5500 max wot revs, how loaded was the toon ?

Happy Boating

 

[jhuds4]

Do you know what's the min-max wot rpm range for that 4 strokes 115 HP engine ?

Which pitch is the current installed 3 blade prop ?

How loaded do you like go boating, lightly, medium or heavily loaded ?

When achieved 5500 max wot revs, how loaded was the toon ?

Happy Boating

I don't have the manual on me but I think the Max is 6000 rpm. I don't know what pitch the prop currently has. I like to load the boat up with a lot of people, 21mph @5500rpm was done with just me in the boat.

 

[roscoe]

What ever size is on there now, switch to the Spitfire 4 blade in the same pitch. Possibly drop the pitch by one if you like.

Your never going to make it faster by more than 1 or 2 mph, if you are lucky.
Going to a four blade will give you a bit more thrust when trying to maneuver that barge.

There a bigger things to worry about, like if you have enough ice for the cooler.

 

[jimmbo]

If you want to go faster, put the Wife, kids and Mother in law ashore, Mistresses and Girlfriends can remain aboard. Make sure the engine height is correct, load on boat properly located, engine trimmed optimally, and proper propeller. Any speed increase beyond that will require more horsepower

 

[Sea Rider]

If that engine revs 5500 rpm with one up, don't want to imagine with a lot. Definitely revving way under the lugging side which is no bueno. Need a prop to rev at full wot rpm range when lightly loaded, can add more boaters till wot range drops to middle range to still have some boating fun. The rest can stay at shore zipping cold ones while seing toon cruise or will end screwing your nice boating day lugging your engine badly if wanting to join for a free ride. LOL!!

Happy Boating

 

[ahicks]

I would add that you don't want to trust a Merc. rep when seeking a new prop like that. You need to find out what prop is on it to prevent the potential for an "oops" sorry, we don't take used props back. I will guarantee you that he will not take a wrong guess back for refund, exchange, or credit. Basically, he has no skin in the game....

I have a Honda 90 on a fairly light 24' 'toon (same 6k max rpm). With a 13' pitch it's turning about 6100 at 25mph. Good bottom end, good mid range, and gets to top end without hesitation - with just me on the boat.

I bought a 15" prop for it, that turns 5500 at WOT. Still has great low and mid range (not much change) but now it takes a bit to get to top speed. It's slower from maybe 22mph, to it's new top speed, which is faster, now 27mph.

I like the 15" prop better. It's quieter at top speed, with little performance loss in low and mid range. Plenty of zip for yanking the kids around on a tube.

Point being, unlike the 2 strokes, I think the 4 strokes are happier when turned about 500 rpm below max.

 

[Faztbullet]

First make sure replacement prop is for a toon as big difference in prop designs.

https://www.boatingmag.com/boats/pontoon-boat-props-no-mickey-mouse-affair

 

[jhuds4]

I would add that you don't want to trust a Merc. rep when seeking a new prop like that. You need to find out what prop is on it to prevent the potential for an "oops" sorry, we don't take used props back. I will guarantee you that he will not take a wrong guess back for refund, exchange, or credit. Basically, he has no skin in the game....

I have a Honda 90 on a fairly light 24' 'toon (same 6k max rpm). With a 13' pitch it's turning about 6100 at 25mph. Good bottom end, good mid range, and gets to top end without hesitation - with just me on the boat.

I bought a 15" prop for it, that turns 5500 at WOT. Still has great low and mid range (not much change) but now it takes a bit to get to top speed. It's slower from maybe 22mph, to it's new top speed, which is faster, now 27mph.

I like the 15" prop better. It's quieter at top speed, with little performance loss in low and mid range. Plenty of zip for yanking the kids around on a tube.

Point being, unlike the 2 strokes, I think the 4 strokes are happier when turned about 500 rpm below max.

Wow that'll scoot! I guess mine is pretty loaded down- I believe it's a 24' 2005 fisher freedom deluxe fishing package or something like that. My grandfather bought it but never uses it anymore so my Dad and I take care of it now. I had two people on the boat one time and one person on a knee board and it wouldn't get over 17mph and would max out at 5200 rpm. Just feel like I could be getting more out of that 115hp motor you know?

 

[ahicks]

Well, you need to decide where your priorities are. If you want to max performance out with 2 people on board while pulling a knee board, that's entirely possible! Doing that, you just take what you get the rest of the time when it's not being used that way. You may for instance, be required to use just partial throttle to keep from over revving the engine when lightly loaded w/o load of the knee board?

Point is props are a compromise, and can be optimized to an owners particular needs.

Betting you could find a prop that will turn right at 6k with 2 people on board while pulling a knee board. That prop should provide noticeable differences in the performance you have now.

So getting back to your boat, if you're turning 5200 now and want to get that closer to 6k while pulling a knee board, a prop with 2" less pitch should put you pretty close. Where you end up for top speed with that knee board is anyone's guess, but will likely be faster than 17mph. WAG would be 19mph maybe?

Our boat, pulling an 8 year old on a tube, is easily capable of going as fast as I dare. Pulling a 300 pounder, I'm running pretty much wide open! I can count on one hand the number of times I've been called on to pull this guy to date, so I don't believe it's in our best interest to set the boat up just for the conditions we see while pulling him. My priorities, for the time being anyway, are more about cruising and pulling an occasional light weight at 15mph.

 

[Sea Rider]

Boating with 2 up while pulling a third boater on a tube or even a skier behind the transom is worse that boating with same 3 up on deck. Tuber or skier drag will kill the wot rpm badly, much worse if tube is badly inflated and skier is a heavy weight champ.

Happy Boating