Yet another prop change....heavy boat=big ears?

[WTP07]

In an effort to get this big heavy beast up to the correct RPM's, and hopefully a MPH or 2 more, I did some consulting with a local prop guru.

I was using a 4 blade aluminum 15" x 16p. This would get me 4100 RPM's at around 27 MPH, depending on conditions. Then I bent that one slightly. Don't ask. I had to do some fence repair too. :smt021

Fortunately I had a spare for last weekend's Pottahawk nonsense. It is the 14.75" x 19P shown below. This topped me out at about 3200 RPM and around 22 MPH.

So after consulting with said guru, he ordered me this beast:

16" x 14p 3 blade Mercury Black Max aluminum. Check out those ears! They're HUGE! I will get it on the water tomorrow and let you all know how this changes things.

Does this concern anyone? Look at how close it is to the anode/cavitation plate. it's about 1/2" to 3/4" away. Should I be concerned with this?:smt100

Updates to follow

 

[sprink56]

Do you not run the "fin" or is it off for photo purposes?

That prop may be the answer for you...fitting between the 2 RPM exremes.

 

[WTP07]

Do you not run the "fin" or is it off for photo purposes?

I have never had a "fin" type anode there, it has always been the flat one.

That prop may be the answer for you...fitting between the 2 RPM exremes.

Actually, the 4100 RPM's were too low as well, they need to be between 4400 and 4600 for this engine.

I hope to get there with a decent top speed and maybe holding on plane at a lower speed with the big ears.

Cheers,

Randy.

 

[tmhudson2]

If your new prop is 14.75" diameter, and the old one was 15" diameter, then the new prop ought to give you more clearance between the prop blade tip and the cavitation plate (by 1/8"). I assume your question has to do with the fact that the bigger blades will be moving more water, and so may creatre greater friction loss even though the clearance has increased a smidgen.

 

[WTP07]

If your new prop is 14.75" diameter, and the old one was 15" diameter, then the new prop ought to give you more clearance between the prop blade tip and the cavitation plate (by 1/8"). I assume your question has to do with the fact that the bigger blades will be moving more water, and so may creatre greater friction loss even though the clearance has increased a smidgen.

No, actually the prop I was running was a 15" x 16P 4 blade. I had the 14.75" one on just for last weekend so I could get out while my new one was on order. The new prop is 16" x 14p. So I increased 1.25" from the "temp" 3 blade and 1" from the 4 blade I was originally running. So it should actually be 1/2" closer than the 4 blade....

 

[Tail Chaser 661]

I used the same prop for 3 seasons. I was pampering my Alpha 1. The 14"P offsets that huge blade area. My goal was 20kts at 3000 rpm. Came up short of that. A 16x16 Alum would be sweet if you could spin it. They have worked good on some CSR members 8' beam 26'classics. 15.5 x 15 stainless seems to be another good option.

 

[WTP07]

Tailchaser,

What was your RPM at WOT with that prop?

I bet you could run a 16" x 29p with that new beast of an engine you're putting in!!

 

[Henry Boyd]

TC,

While we are on a prop discussion what are you planning to use on the new engine? The 280 (2.0:1 drive) used a 22p cupped set. What did you come up with?

Henry

 

[Tail Chaser 661]

TC,

While we are on a prop discussion what are you planning to use on the new engine? The 280 (2.0:1 drive) used a 22p cupped set. What did you come up with?

Henry

2.20:1 with a cupped 26" pitch. Thats per CSR member keokie's specs. Who did a lot of homework :thumbsup:
Merc specs out with the same prop. 26' boat. total gross wgt 9000lbs.
That gear ratio really puts the TQ to the prop. A remedy used to help out under powered engines.

 

[Tail Chaser 661]

Tailchaser,

What was your RPM at WOT with that prop?

I bet you could run a 16" x 29p with that new beast of an engine you're putting in!!

I never ran WOT with that prop. Never had glassy waters either. I actually did bring my rpm's up to 4400 fairly easy doing 32 mph into some 3' swells when the girlfriend pissed me off :lol: That was the funnest part of the two day trip.
Some approx cruise specs were...3000 rpm was doing like 16 mph. 3400 rpm was 20 mph or close to it. Always in rough water. Broke my Alpha at 50 hrs due to a jerk mechanic. Never trusted the Alpha since.

15.25 x 26P is all I can do with the 8.1 :huh::smt089
A CSR member That had a 502 ci 83 26' DA was doing 23 mph at 2500 rpm, 30 mph at 3000rpm, and 35 mph at 3500 rpm getting 2.3 mpg. His top speed was 53 mph touching the 5k rev limiter. Thats with a double cupped 26"P
The 496ci has more mid range tq and less top end power then the 502ci. I can only hope to match his 502ci Mid range cruise numbers of 3500 rpm and below.
I could not find a turn key 502ci anywhere. Rumor has it, The 8.1 is a nicer engine :huh: Quicker reving and smoother idle.

 

[sprink56]

Guys,

Keokie has this swap into these boats "nailed shut", If he says it's so I would certainly give a try ahead of any thing else. He is always factual and tells it like "truth fact and real" and if you don't believe it...hide and watch.:thumbsup:

 

[Tail Chaser 661]

Guys,

Keokie has this swap into these boats "nailed shut", If he says it's so I would certainly give a try ahead of any thing else. He is always factual and tells it like "truth fact and real" and if you don't believe it...hide and watch.:thumbsup:

I think the finishing punch line should be... Catch him if you can :lol::lol::lol:
He talked to numerous performance boat guys and Merc tech people coming up with the 2.20:1 GR.
Results... A slower turning high pitch prop performs better then spinning a less pitch prop faster.
Problem with the 5.7 26' DA Alpha Gen 1 combo.
Not enough engine tq. And not a strong enough drive to push a big prop with lots of pitch.

 

[WTP07]

All I can say is.....WOW

What a difference!! This thing JUMPS up on plane now, I get to 4400 RPM without trimming up, and the acceleration difference is huge! I wasn't able to check out where the top end was, but I got up to 28 MPH on the GPS at 4400 RPM, so with trim, I should be get back up over 30 MPH again. If the lake lays down tomorrow I will give'r another go.

Cheers,

Randy.

 

[Tail Chaser 661]

Re: All I can say is.....WOW

What a difference!! This thing JUMPS up on plane now, I get to 4400 RPM without trimming up, and the acceleration difference is huge! I wasn't able to check out where the top end was, but I got up to 28 MPH on the GPS at 4400 RPM, so with trim, I should be get back up over 30 MPH again. If the lake lays down tomorrow I will give'r another go.

Cheers,

Randy.

Very cool :thumbsup:
Now with some trim adjustment, Maybe you can spin that 14"P prop over 4600rpm. Then you could try the 16 x 16 Alum. But Your Alpha drive may not think so.
That hole in the water has a healthy appetite. Its probably time to feed it again :lol::smt043

 

[keokie]

Tail and Sprink,

Thanks for the compliments. What I learned came from a group of us family and friends that combined to spend an unbelievable amount of time and money on classic 260's.

TC, you will not be disappointed in the performance.

One thing though, I saw somewhere else in another thread where you mentioned not being able to use the BIII water pick up with a 496. The twin 496's in my 310 pick up through outdrive with no problems. Those 496 sea pumps are junk (and expensive at that), however. They need stainless wear plates, or they will fail early.

 

[Tail Chaser 661]

Tail and Sprink,

Thanks for the compliments. What I learned came from a group of us family and friends that combined to spend an unbelievable amount of time and money on classic 260's.

TC, you will not be disappointed in the performance.

One thing though, I saw somewhere else in another thread where you mentioned not being able to use the BIII water pick up with a 496. The twin 496's in my 310 pick up through outdrive with no problems. Those 496 sea pumps are junk (and expensive at that), however. They need stainless wear plates, or they will fail early.

Giving credit where credit is due. I really appreciate the valuable info you have given me keokie :thumbsup:
Another member with a 496 mentioned the B3 water inlet is not used. There has been a couple of other post where the inlets were getting blocked etc. The parts schematics show what looks like a reducer or something similar in the transom assembly.:huh: The hose barb looks plastic, But I have not taken everything out of the boxes yet to see if anything really looks like a poor design. I sure have lost/wasted a bunch of time checking out thru hull scoopers, strainers and how I want to route the mess :smt013
Did you run the B3 water intake with your Classic DA with the 502ci? Thanks again for the info keokie:thumbsup:

 

[Henry Boyd]

Keokie,

In our neck of the woods, the Merc techs like to by pass the drive pick ups with a through hull. I still have the drive pick up attached but with a through hull in between. I was having temp issues before we did this and nothing since.

Henry

 

[Tail Chaser 661]

Keokie,

In our neck of the woods, the Merc techs like to by pass the drive pick ups with a through hull. I still have the drive pick up attached but with a through hull in between. I was having temp issues before we did this and nothing since.

Henry

I was being shy :grin: I had not got around to asking you if there was a water block off kit for the B3 or if the water hoses were run the way you just said. Lots of google searching had been turning up nothing.
Henry, Do you have a raw water strainer/filter installed on your 8.1 ? My searches did come up with fresh water boats getting into sandbars etc. Sand and pebbles then wreck havoc on the cooling systems.
One other thing Henry. Are you using a basic bronze 1 1/4" thru hull? Or did they install the scupper type thru hull?
Thanks for any info :thumbsup:

 

[keokie]

TC, Yes, I ran the 502 water pick up through the drive.

Henry, the Merc techs may be recommending the through hull pick up to reduce flow resistance and take advantage of the force of the scoop at speed. The difficulty with the pumps on the 496's (and Merc bragged about this) is the metallurgy. The bronze they used to make the pumps is too soft. The end plates wear prematurely allowing the pumps to suck air which greatly decreases the flow rate. This in turn causes cooling problems.

I had wear plates made out of inconel, and now the pumps perform very well. A scoop might mitigate a good bit of the problem with the pump design, but ultimately does not cure it.

The Merc pumps are also quite expensive. Something like $400. The fix is widely unknown, but I can tell you from experience it works. If a boat was left in water permanently, there might be electrolysis issues. However, mine has spend quite a bit of time in slips with no adverse events, and the pumps flow very well now.

 

[keokie]

TC, Yes, I ran the 502 water pick up through the drive.

Henry, the Merc techs may be recommending the through hull pick up to reduce flow resistance and take advantage of the force of the scoop at speed. The difficulty with the pumps on the 496's (and Merc bragged about this) is the metallurgy. The bronze they used to make the pumps is too soft. The end plates wear prematurely allowing the pumps to suck air which greatly decreases the flow rate. This in turn causes cooling problems.

I had wear plates made out of inconel, and now the pumps perform very well. A scoop might mitigate a good bit of the problem with the pump design, but ultimately does not cure it.

The Merc pumps are also quite expensive. Something like $400. The fix is widely unknown, but I can tell you from experience it works. If a boat was left in water permanently, there might be electrolysis issues. However, mine has spend quite a bit of time in slips with no adverse events, and the pumps flow very well now.