Good evening all. I’m new to the forum and also the Bennington pontoons. Recently picked up a 2013 Bennington 2375 GCW with Mercury 115. Cruise around the lake all day no problem, wanted to open her up, going full throttle RPM gauge goes right on to 7k. Download a RPM app, got 16MPH max. All this was with 4 adults and 4 small kids 1/2 to 3/4 tank. Boat would not plain out whatsoever. Pulled the prop today to check bushing. All seems solid and no spinning (basically corroded together). I’m stumped. Prop is a BlackMax 77342A45 15P. Engine is clean, fires up perfectly, idles perfectly, accelerates great. Keeping it between 5-6k rpm, I’m running 13mph. Am I missing something?
WOT going straight to 7k
- Thread starter JJmathis
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Remediation
Well-Known Member
You have a very heavy boat with a heavy load and an 115HP engine. That engine is undersized for your setup. The high rpm could be from the prop cavitating. Even with a great prop that engine will never give you the performance that you are looking to achieve. Understand what you have and enjoy the boat.
Thank you Remediation, I agree, heavy boat, heavy load. I’m not an expert but I think it should still get up on plain, the engine is from factory. Should push the boat along just fine but it shouldn’t run straight up to 7k rpm. Could be some cavitation, I’m going back out this week with someone more experienced to see what they think.
Remediation
Well-Known Member
Is it a 2 toon, 3 toon or elliptical toons?
Jack M
Moderator
Check with Ken at propgods.com
Jack M
Moderator
You mentioned you have a 15 pitch, what's the diameter?
Jack M
Moderator
I have a Bennington " suggested " prop chart. Suggested size for a 23 ft with a 115 is 13.8X13
Jack M
Moderator
Ken can get you dialed in , give him a call or send him an email
My 22 GSR with Sea Legs, 2 toons, and 115hp could never could get up on plain. It just didn’t have the floatation, or HP, and would plow through the water versus getting on top. Great for cruising, but people in the front would occasionally get wet if I hit a large wave wrong given how it floated in the water.
Nautical
Well-Known Member
My first thought was that the prop was swapped with the wrong one before you bought it and that it needs a larger pitch but it seems that the 15 is enough if not already too much. I'm betting there is something else going on here. Even though it seems like it's not slipping when examined by hand, it could still be slipping under load - OR - maybe the slippage is occurring internally where you can't see it? That high an RPM with that high a pitch yielding that poor performance means there is definitely something not right and you should get it checked sooner rather than later.
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I do plan to get a couple different props just to test them out. Will definitely pick up the 13p 13.8 dia. Seen this one suggested a lot.
I agree, I do plan on having it checked out more in depth. I think there’s something going on. Unfortunately it wasn’t as simple as the prop bushing.
I assume you have a 115hp 4 stroke? Its not a 2 stroke is it? They still made the optimax DFI back in those years. Reason why i ask is RPM range. 4 stroke is 5300-6000 WOT and the Opti is Up to 5750 or something like that.
SO it your hitting 7000, you well over-revving the motor and shouldn't be anywhere near that with a 15 pitch prop. I would think you have a bad hub that won't slip under light conditions but will fail under any heavy load / torque of the motor.
If you leave the trim all the way down or 3/4 of the way down so the nose of the boat is in the water, can you still hit those RPM? That can help rule out any cavitation / ventilation issues. Just make sure you do it in calm water as you don't want to take a wave over the decking and dent any of your panels or gate.
Do you know what hole the motor is mounted in?
SO it your hitting 7000, you well over-revving the motor and shouldn't be anywhere near that with a 15 pitch prop. I would think you have a bad hub that won't slip under light conditions but will fail under any heavy load / torque of the motor.
If you leave the trim all the way down or 3/4 of the way down so the nose of the boat is in the water, can you still hit those RPM? That can help rule out any cavitation / ventilation issues. Just make sure you do it in calm water as you don't want to take a wave over the decking and dent any of your panels or gate.
Do you know what hole the motor is mounted in?
DVW
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I assume you downloaded a boat speed (mph) app not engine speed (rpm). Your boat speed is somewhat proportional to engine speed. This would cause me to rule out propeller aeration (cavitation). Are you sure you got a prop with a 15 inch pitch. That does not seen to add up.
BigKahuna
Well-Known Member
Correct me if I'm wrong. I always thought that a 2 pontoon boat never really gets up on plane! It just pushes through the water......
DVW
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You are correct but even modest powered pontoons will appear to get up on plane. The bow will rise and then at some speed the bow will fall with only modest throttle input. This is a good topic for another thread.
I've wrote about / had this problem before too. I've got a 200 horsepower F200 Yamaha on my 25 foot Q series with a Tower. It does better than your boat does but still you have to baby the throttle all the way up to wide open or it will just cavitate for sure. I can get mine up into the low 30s mph wise. I've learned to live with it as we don't do as much tubing and skiing as we used to but have always been a little aggravated by it...
Fullcircle22
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Just to add something, before my Bennington I had a Sunchaser 22 regular 2 tube with a 115 yammy 4 stroke. It would run about 23mph with 2 people and full fuel. That being said it had an aluminum Solas "pontoon prop"(Mickey Mouse ears for non-planning style boats) and when I put the standard design planning hull prop on it with the same specs it slowed down mph and raised rpm. If the boat doesn't move fast enough to flow enough water over the prop it will boil the water causing cavitation. Just my 2 cents.