Newbie here, help with 4 blade Rpm'S

[giegerkey]

I have a 2005 Bentley 200 fish pontoon boat with a 60 HP Bigfoot. I recently changed the original prop from a 3 blade 13.8x11 to a 4 blade 13.8x10. I was looking to get more power on the water as well as lower and middle performance. I definitely got it. The new prop raised the rpm from 5500 WOT to 6200 WOT. To high!!!. The speed has always been about 17 to 19 no mater what prop I use. I am thinking that it is unusual that the 4 blade raised the rpm up by 700... So here's the issue I have. I have another 4 blade 13.8x13 prop that I tried out today and it was pushing the rpm at 4200 WOT at 17 MPH. So I went from a 10 pitch at 6200 to a 13 pitch at 4200 that's 3 pitches up and 2000 rpm's.

What size 4 blade prop do I need to achieve a good running WOT?

 

[Sea Rider]

What's the factory min-max wot rpm range for that 60 HP to start with ? What are you trying to achieve, better top end speed or better hole shot ?

There's no perfect prop match on first attempt, usually on second if not on third one. Nobody said boating was a cheap sport. LOL!!

Happy Boating

 

[giegerkey]

Min 5500 Max 6000. Can't seem to achieve it with a four blade prop, and the next purchase will be my 4th prop. $600.00 in props aint cheap. That's why I'm asking the question so the correct prop will be purchased next. I have talked on the phone to Mercury, Turning point, and Michigan wheel. Mercury and turning point did not want to commit in any way. Michigan wheel said the 11 or 12 will be the correct pitch. I already knew that... I have a planing fin on my motor. With the four blade the boat will get on plane, with the three blade it will not. I am looking to stay on plane and fantastic hole shot without going over my limit.
Thanks

 

[ahicks]

"Bigfoot" option is available on both 2 stroke and 4 stroke engines. If this is the 2 stroke, you're likely looking for something that will turn closer to 6k. If it's the 4 stroke, thinking you'll find 5500 closer to the sweet spot. The 5500 target will give you a quieter ride while providing nearly identical performance as it would at 6k

Blade style and shape have a LOT to do with this, and is likely the biggest reason for your results. If you want predictable results based on something you have, you need to stay with similar style props.

Struggling with the comment regarding planing "the four blade the boat will get on plane, with the three blade it will not". You're saying the 3 blade will go 17mph and the boat is not on plane yet? That would be a first for me...

Throw that planing fin away. It's just creating drag and/or covering up a setup mistake. It should not be necessary, especially when seeking performance - in my experience anyway.

If your 4 blade 13.8x10 turned 6200, that's over, but an excellent reference point for selecting the prop to put you int the range you're looking for. It's actually pretty darn close! That's actually the size I would have gone for when making a 3 to 4 blade switch.

Anyway, the 10" was close, so jumping all the way up to a 13" gave predictable results - WAY too big a jump when you are only 200rpm or so over target.

My vote/best GUESS, I'm with the rep at Michigan Wheel. 11" for a target of something just under 6k, or maybe the 12" for something a little more conservative (maybe just over 5k) - and this is assuming you stay with the same series of prop as the 13.8x10 that's turning 6200. That's important when looking for predictable results.

 

[giegerkey]

ahicks, Thanks for your reply. I needed to here that from someone other than a salesman or rep. It is a four stroke EFI and performs outstandingly for my purpose. I have never had regrets on this boat or motor. As far as the planing fin, without it the rear of the pontoons just push further down into the water and it is does not plane. That is the reason why I put it on. As far as the prop recommendation I am leaning to the 11 because of fear of blowing another hundred bucks on the 12. But, I would like to see the 12 in action. So still on the fence but closer to a purchase.
FYI, I use my pontoon boat mostly on the St Johns river between lake Monroe and lake Jesup. I fish the shallow estuaries between the lakes and the four blade prop has been a life saver on several occasions. Although we are not on the coast the tide is relevant [about a foot high and low] in this area and can get you into shallow water trouble if your not careful. I also tow it to the ponce inlet in new Smyrna beach for some great fishing and sightseeing of dolphins, large ships, tourists and of course disappearing island. Thank you for your input.
Joe

 

[Sea Rider]

Some issues to add to the equation ;

How loaded do you like to go boating, say light, medium light, fully loaded ?
What's the max passenger and HP capacity that toon can handle as per tech plate if having one ?

Toons achieves extraordinary hull drag compared to standard one piece hulls, will be interesting to know if the toon was ever able to fully plane out or achieved just fast displacement speed with a 60 HP.

Correct engine height on transom along well trim accounts for least water drag on lower tail which is ideal to achieve specially if running under powered OB's. If the doel fin does not ride parallel to water level when combo is on its way but does at an angle the lower leg drag will be increased and combo will inevitably be slowed down. Trim OB to sit at 90 deg on transom and distribute deck weight evenly for better water performance.

Can't see why a 3 blade alum prop won't perform top, you need to prop an OB right to rev to at least middle to max wot rpm range as usually loaded, the issue is that near everybody is going from its current 3 blade prop to 4 blade ones. Is it some sort of fashion issue going that route. Seems that with 4 blade props you need to test way more props than with 3 blade ones while the money thrown into the deep blue will keep rising.

Back in the good old boasting days when there were no 4 blades available everyone played with pitch along a tach and that was it. For me 3 blade OEM props with different pitches is the way to play with...

Happy Boating

 

[giegerkey]

An essay by me. please disregard if not interested.

I have a large 8 x 20 square aluminum frame with sheets of plywood attached to it and carpet attached to the wood. On top of that I have a seating arrangement with square furniture similar to a living room as well as a dash board with instruments and electronics galore. Behind all of this sits a relatively small outboard motor with a 25 gallon fuel tank, twin batts, fuel filters, 110 battery charger and an underway battery charger. Mid way there is a thing called a Bimini top that is nothing more than a huge incredibly heavy and cumbersome umbrella. Oh, I love this Bimini top so much I added another one to the front!!! and don't forget the 200 pounds of gear for any occasion that pops up from fishing to having drinks/cook outs to grand kids and dogs. All of this sits on two 25" round tubes that by design barely displace water. The only round, tubed ship I have ever seen is a submarine. I get a top speed of 17 MPH maybe 18 or 19 on a glorious day. The captain of this craft [me] was never really happy with his ship until the day he stumbled across a four blade prop. By chance he was launching next to a guy with almost the exact same set up with a four blade prop and a doel fin. Short conversation later I was convinced to take a chance. The next weekend I had for the first time since I bought the boat new in 2005 what I wanted. A little bit of fun in an otherwise very dull pontoon world.
I ordered the 4 blade 13.7/8 x 11 prop. I will post results when I have them. Thank you both for your input! Very, very helpful!
Joe

 

[ahicks]

Best of luck with the new prop. Hopefully, it'll do exactly what you're expecting it to do! Please keep us posted.