JonathanEngr
Seaman
- Joined
- Jun 10, 2009
- Messages
- 66
Okay--I had some time today to take my pontoon out and do some speed tests. Don't get too excited... we're talking 16-17mph here 
My pontoon is a 2002 24-foot Bentley 824 with a 50-hp Mercury motor. It's perfect for what my wife and I wanted, and the kids (5 & 4) think they're zipping across the water at 100 mph on their towables (hopefully we've got another 2-3 years before they say, "Dad, this is BORING!"). However, I'm a tinkerer, and I want to do a few little things to see if I can get 20-21 mph out of this baby.
Here's the problem. During testing with my GPS..., and I could consistently get 16-17 mph at 4500 rpm. Into the wind, against the wind, smooth water, calm water--whatever (I did hit 18 mph a couple of times. They need to put some hills on these lakes!). The speed increases every 1000 rpm were pretty proportional, so I assume I have no "prop slip" for the most part. Is this correct? However, here's the doozy....
From 4500 rpm to WOT (5500 rpm), there's zero increase in speed. Zilch, zero, nada. It always seemed to me that from 4500-5500 made little to no difference, and I confirmed that today with the GPS (other than a louder engine!). Sooooo... what could be the problem?
I'm sorry for the lack of info, but I'll check my prop tomorrow in the sunlight and get the size and pitch--I assume they're stamped somewhere on the prop? I also try to get the engine details, but I assume a 50-hp Mercury is pretty standard? Also, I'll try to take some pics to post on here, as well. The prop is aluminum, and the paint is wearing off. I just bought the boat and the prop was supposedly new as of the beginning of this year. It doesn't look damaged from a distant inspection, but I'll look closer tomorrow.
Questions:
1) Is this normal to see a zero speed increase at higher RPM's? If I'm hitting 16-17 mph at 4500, should I be getting 20-21 mph at 5500?
2) I know it's a 'toon, but will props (sized to top out at the rec'd 5500 rpm) that are higher-performance like cupped props (Hustler, etc.), etc., make a difference? I saw in a post somewhere on here that cupped props give you another inch of pitch... true? Not true?
3) I assume SS props on 'toons are a waste of money. Am I correct that SS props are best for higher HP applications and quick launches since they flex very little when power is applied? Or do they also help at top speed?
4) Does it seem feasible to hit 20-21 mph in a boat like this? I have *no* idea what the weight of the boat is. Other than picking it up and standing on the bathroom scales <grin>, how can I find out? Are boats required to have the weight stamped on them? I can say that the trailer that came with this boat is single axle, non-braking, and it rides it very well. I ask this because I noticed another similar post where the guy had a pretty heavy pontoon which made a big difference.
5) Do things like larger hydrofoils on the engine really help to avoid cavitation, prop blow out (what is that?) and such? Could this be my problem? Here's the link to one I saw for my engine:
http://www.westmarine.com/1/1/8438-...ngine-capacity-from-sport-marine-technol.html
Anyway, I'm going to do a few different things and see what it does to my top-end. I just don't want to go stabbing in the dark... I need some good, expert educated guesses!
Thanks for any input anyone can give me.
My pontoon is a 2002 24-foot Bentley 824 with a 50-hp Mercury motor. It's perfect for what my wife and I wanted, and the kids (5 & 4) think they're zipping across the water at 100 mph on their towables (hopefully we've got another 2-3 years before they say, "Dad, this is BORING!"). However, I'm a tinkerer, and I want to do a few little things to see if I can get 20-21 mph out of this baby.
Here's the problem. During testing with my GPS..., and I could consistently get 16-17 mph at 4500 rpm. Into the wind, against the wind, smooth water, calm water--whatever (I did hit 18 mph a couple of times. They need to put some hills on these lakes!). The speed increases every 1000 rpm were pretty proportional, so I assume I have no "prop slip" for the most part. Is this correct? However, here's the doozy....
From 4500 rpm to WOT (5500 rpm), there's zero increase in speed. Zilch, zero, nada. It always seemed to me that from 4500-5500 made little to no difference, and I confirmed that today with the GPS (other than a louder engine!). Sooooo... what could be the problem?
I'm sorry for the lack of info, but I'll check my prop tomorrow in the sunlight and get the size and pitch--I assume they're stamped somewhere on the prop? I also try to get the engine details, but I assume a 50-hp Mercury is pretty standard? Also, I'll try to take some pics to post on here, as well. The prop is aluminum, and the paint is wearing off. I just bought the boat and the prop was supposedly new as of the beginning of this year. It doesn't look damaged from a distant inspection, but I'll look closer tomorrow.
Questions:
1) Is this normal to see a zero speed increase at higher RPM's? If I'm hitting 16-17 mph at 4500, should I be getting 20-21 mph at 5500?
2) I know it's a 'toon, but will props (sized to top out at the rec'd 5500 rpm) that are higher-performance like cupped props (Hustler, etc.), etc., make a difference? I saw in a post somewhere on here that cupped props give you another inch of pitch... true? Not true?
3) I assume SS props on 'toons are a waste of money. Am I correct that SS props are best for higher HP applications and quick launches since they flex very little when power is applied? Or do they also help at top speed?
4) Does it seem feasible to hit 20-21 mph in a boat like this? I have *no* idea what the weight of the boat is. Other than picking it up and standing on the bathroom scales <grin>, how can I find out? Are boats required to have the weight stamped on them? I can say that the trailer that came with this boat is single axle, non-braking, and it rides it very well. I ask this because I noticed another similar post where the guy had a pretty heavy pontoon which made a big difference.
5) Do things like larger hydrofoils on the engine really help to avoid cavitation, prop blow out (what is that?) and such? Could this be my problem? Here's the link to one I saw for my engine:
http://www.westmarine.com/1/1/8438-...ngine-capacity-from-sport-marine-technol.html
Anyway, I'm going to do a few different things and see what it does to my top-end. I just don't want to go stabbing in the dark... I need some good, expert educated guesses!
Thanks for any input anyone can give me.
