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2250RL Performance Issues

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WI-RiverRat

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Hi,

I'm brand new to the Bennington forums, but I used to spend a lot of time over at PDB Forums years back.   Love the boat, the speed, not so much.  Should have held out for a 150HP, but it was a great deal and have had it for years.

Like the title says, we've got a 2250RL with a Mercury 4 Stroke 115HP.  It's always been a good runner, but never has had the performance numbers that it should.  I've never been able to get it up to 6000rpm.  I've had three different boats Outboard Tri-hull, I/O Deep V and now Outboard Pontoon and I know the "exact right" prop can make a world of difference....

When I bought the boat (used) it had a 15P Alum prop on it (Merc, I believe) I got the following speed vs. rpm curve.  Speed was gps.  The figures below are the average of a number of runs.

RPM     MPH

2000     7.9

2500     10.8

3000     14.6

3500     16.7

4000     19.6

4400     21.2 

I knew I needed to be a LOT closer to 6000rpm at WOT, motor was lugging etc.  So I changed to a 13P Merc Alum.  prop.  and get the following:

RPM     MPH

2000       7.8

2500       9.2

3000     13.3

3500     15.1

4000     17.6

4500     19.4

4800     21.2  (sometimes, with the wind 4900 to 5000rpm)

It runs better, but still not what it should be.  In looking at old test reports etc., pontoon waterglide, 3 rd toons etc all way too expensive I found lots of reports of 15P props and boats with 115HP clocking 24,- 28MPH.  A Yamaha report of a 2274GLi w/ a Yamaha 115 14.25 x 14 SS topped out at 27MPH.

Any thoughts or recommendations on props or other ideas?

Thanks in advance for your advice and ideas!   Looks like a great forum.
 
Welcome and do you have strakes? Are you sure the throttle is opening all the way. Without strakes you'll just be plowing through the water.
 
Wi-RiverRat.  I have a 2012 2275RL with a Yamaha F115.  I never tried any other prop than the one my dealer placed on it, an aluminum 13.5 x 15.  My current stats are with just me and the wife WOT are 24.5 mph at 5400 rpm
 
Welcome and thanks for providing such good data. You're obviously working hard at it!

Can you also tell us which hole your motor is mounted on? It would be good to compare against other 22'/115hp's such as Link's.
 
Thanks for the info.  No strakes and the engine is mounted as far down as possible..  I will try and get the prop dia. this evening.  A couple of other bits of info that I forgot to include last night.  When I test drove the boat before I bought it, the engine would not spin over 3000rpm so my offer to the owner was 'take it back to the dealer, have them fix this issue and I'll buy the boat'.  Dealer said it was dirty fuel injector(s).  Don't really know what they did or didn't do, but it bring rpms up about 1000.

Normal usage includes tubing and sking with 3 - 4 adults on the boat.  Kids are now 16 & 14 and boat is too slow.  I have to be aware not to hold WOT too long (30+ min) without a break or will trip overheat warning horn.  Interestingly enough, adding Marvel Mystery Oil to the gas seems to abate the overheating issue but that's treating the symptom, not the cause.

I think I'm getting full throttle response, but perhaps not.  Any thoughts on how I could check this?  I have some photos of the motor setup that I couldn't find last night.

Link - Your response gives me hope.   If I could get 6000rpm and around 25mph,  then I can start thinking about a SS prop. 
 
Hi I will give you specs for my pontoon.  22ft SL,  Yamaha 115fl.  13.5x15 yamaha aluminum prop and strakes.  2 adults, 1/2 tank of gas.  At 6000 rpm  I am at 33mph on the gps.   1 person onboard I am at 35mph on the gps.  Just this last weekend had 8 adults on board and at 20 mph at 5500 rpm.  Hope this helps.  I should add that this is a twin tube pontoon.
 
Managed to dig the original prop out of the boat ( I keep it as a spare )  It's marked 16.75 x 15P.  I see Link and Dano are running 13.5 x 15P  quite a difference.  Thanks Dano - every data point helps!
 
Not sure 16.75 diameter would even fit, so something doesn't sound right there. Maybe just compare measurement of diameter across the blades to see for sure what it is.
 
2275 RLi here. With 2 25" tubes, my Merc 115 with a 13 pitch prop (alum Merc) pushed it to 28 mph at 6400 rpms with just me aboard. I just added an Express Tube.

Now, with a 15 pitch prop (again, Merc alum.) I am still maxed out at 28 mph at 6200 rpms. My ride and handling have improved tremendously, but no gain in top speed.

I suspect a mechanical problem continues to manifest itself in your situation.

Hope this helps.
 
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Could be pond scum on the hull... Does it stay in the water all the time? That will cut the speed way down...
 
Keep us posted Wi-riverrat, am looking forward to seeing what the solution was.  Like kaydano the dirty toons was my first suspect but after reading about Marvel Mystery Oil I do suspect the engine has some problems
 
Let me share my latest with you. I have a 2275GCW with a F70. I have been through two props with the dealer. The original,was a 13 5/8 x 13. 5200 rpm clean right at 20 mph, 2 adults and usual gear plus 2 batteries, 29# anchor with 6' stainless lead. I did a lot of research and was told to try the new Talon series. I went with a 13 x 10.5. Gained maybe 100 rpm, no change in speed. The engine is rated up to 6200+ rpms. Full horsepower not reached until 5800 rpms. Based on info here I learned about Ken the prop god. I called him, gave him the stats and after running the numbers he said I needed to try a 14x10 stainless from power tech which he had shipped to me. Once on I turned maybe another 50 rpm and noticed a slight vibration at idle and slightly above. Called Ken, he said we needed to go to a 14 x 9 with a softened hub to eliminate the vibration. The beauty in Ken is he has a $35 exchange program. Two days ago the 14 x 9 arrived after having shipped the original back. Now the results. The engine climbed smooth and effortlessly to 6200+ rpms. I am still turning right at 20 mph but my boat has been in the water since April 25th and has a fine growth layer. So maybe clean I would also gain some top end. However the motor now operates effortlessly at all levels and will turn it's rated rpms. It is mounted in the top hole and is running a little deep. The plate is under the water by a few inches. I think before next season I will have them raise it 1 or 2 holes. Everyone here will tell you stainless is a waste on anything below 115, I would dispute that at this point. I am finally able to turn the proper rpms and my engine is no longer laboring which is worse than over revving. I also appreciate everyone here who shares their experiences.
 
Thanks for giving great detail on what you found and I'm glad to hear Ken was able to help you out. He is certainly the "go to guy" for a lot of people.
 
He got very close on the first try. Then just a $35 exchange to fine tune it.  Awesome!

I don't think stainless had much to do with it.  The design of the prop is likely where the great majority of the difference lies.  There's a lot more to props than diameter and pitch, such as rake angle and cup, the number of blades, shape of the blades, etc.  Glad it works for you, but guessing the exact same thing in aluminum would probably perform so closely on a 70 HP you wouldn't tell the difference.

For example, I have a SS Enertia on my 150 HP.  I hit 41 mph pretty easily.  I also have an aluminum backup prop (a Black Max) that goes just as fast (within 1/2 mph).  But it holds the water like crap.  It ventilates with the slightest amount of up trim.  The Enertia holds the water MUCH better, and has a MUCH bigger trim range before it starts to blow out.  It is by FAR my prop of choice, but not because it's SS, but because of the design.  But even on my 150, the speed difference between the two is negligible. 

Anyway, glad you got it dialed in. There is a lot of talk here about a little scum affecting performance.  Just keep a scrub pad with you, and wipe the scum off every couple weeks while anchored in a cove.  A lot of guys here do that.  They can give you more advice than me.  Our boat is pulled out after each trip.
 
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Thanks for thoughts. I would agree. The stainless feels like it is no work at all from start to top end. The 2 aluminums feel good but would just not spin it up, and I am sure you are correct about the cupping etc. I believe the SS is a WRX. Ken is the best and I have found no one else who will take a prop back for $35. Usually once it's wet it is yours. As it turns out I am now dialed in (until I trade) and I have 2 good spare props on board. I hope I have helped the person who started the topic.
 
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