Formula 27PC Complete Power plant rebuild

HT32BSX115

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My Rinker cuddy has a single 7.4L Bravo 1 at 1.50 ratio, weights 4800 dry and will hit 60 with a 21 pitch 4800 rpm

Sounds like you might have one of your numbers off.......1.5:1, 21p and 4800 results in a theoretical speed of 64mph
http://www.go-fast.com/Prop_Slip_Calculator.htm

To get to 60mph with the above numbers, you would need a slip of 6% ............seems low for a single prop running behind a fairly heavy boat.....

I have found when I get a speed that results in a unusually LOW (or impossible) slip, My RPM or speed measurement

Not saying your numbers are completely wrong, it just seems that the calculated slip is low......
http://www.go-fast.com/boat_speed_predictions.htm


When I had the OMG 460 King Kobra installed in the LIB, the boat did 60 (radar) at 5000 RPM with a 1.43:1 drive and a 20p 3blade ss prop. (19p repitched to 20)
(slip was 9%)
 

alldodge

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I think he means he'll use a 1.5:1 "upper" with a Bravo III "lower" but I am not sure that results in a (over-all) 1.5:1 drive........

I think were getting something mixed. I'm going to buy a brand new from Merc B3XR, just trying to figure out the right ratio. Now Eddie Young states the B3XR is actually a B1XR upper with a standard B3 lower. This is why they will put it behind a 525 or 565 as the largest engines. I thought there was a 1.50 ratio B3XR but this was in error. May go with the 1.65 but jury is still out.

As for my numbers and speed, was watching tach on the boat which could have some error. Was also watching the GPS which should be pretty accurate, I hit 60 but just barely then backed it down, the engine was turning faster then I like to run it.
 

Tail_Gunner

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http://forums.iboats.com/forum/gener...o-3-gear-ratio

If you have time PM hwsiii the guy has a good grasp on prop's

There is something to this prop rpm thing just very little info on it. I cammed my engine and left the drive ratio and prop the same and after a summer noticed the finish had become satin. I had no ideal why and just went on with thing's. last year I tried to polish it up and in the process found out the satin finish was actually micro pitting which I know assume is cavitation burn's. The prop never dulled in the the prior years but the rpm level went from 4900 to 5600 hundred.
 
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alldodge

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http://forums.iboats.com/forum/gener...o-3-gear-ratio

If you have time PM hwsiii the guy has a good grasp on prop's

There is something to this prop rpm thing just very little info on it. I cammed my engine and left the drive ratio and prop the same and after a summer noticed the finish had become satin. I had no ideal why and just went on with thing's. last year I tried to polish it up and in the process found out the satin finish was actually micro pitting which I know assume is cavitation burn's. The prop never dulled in the the prior years but the rpm level went from 4900 to 5600 hundred.

Be worth a try but according to his profile he hasn't posted since July 18, 2014. Thanks
 

alldodge

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Bit of an update: Bought another transom assembly and this time with the sender. It came with the converter module but the anode was also damaged in transit. Was not boxed very well.
Photo421.jpg

Received the replacement anode and the wires were cut. I know I'm getting a very good deal but some things just are not adding up
Photo423.jpg
 

HT32BSX115

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http://forums.iboats.com/forum/gener...o-3-gear-ratio

If you have time PM hwsiii the guy has a good grasp on prop's

There is something to this prop rpm thing just very little info on it. I cammed my engine and left the drive ratio and prop the same and after a summer noticed the finish had become satin. I had no ideal why and just went on with thing's. last year I tried to polish it up and in the process found out the satin finish was actually micro pitting which I know assume is cavitation burn's. The prop never dulled in the the prior years but the rpm level went from 4900 to 5600 hundred.

You're right!

There's quite a bit of engineering info on prop design out there concerning cavitation. Submarine propeller designers take this stuff VERY seriously because ANY cavitation results in loss of efficiency, thrust and MOST important[for a sub] , noise...........so blade angle and prop RPM are extremely important.

I've never really paid any attention to that stuff, but I have noticed where Mercury, Volvo and other drive designers place the drive ratios in reference to MAX engine RPM (I/O, Inboard and outboards incl......EXCLUDING of course, racing and surface drives)

Just about all of then seem to design for an upper limit on prop RPM and max blade angle[pitch] or both...............
 

Tail_Gunner

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You're right!

There's quite a bit of engineering info on prop design out there concerning cavitation. Submarine propeller designers take this stuff VERY seriously because ANY cavitation results in loss of efficiency, thrust and MOST important[for a sub] , noise...........so blade angle and prop RPM are extremely important.

I've never really paid any attention to that stuff, but I have noticed where Mercury, Volvo and other drive designers place the drive ratios in reference to MAX engine RPM (I/O, Inboard and outboards incl......EXCLUDING of course, racing and surface drives)

Just about all of then seem to design for an upper limit on prop RPM and max blade angle[pitch] or both...............



Do you know the math to figure out my blade tip speed..1.66@5600 20 pitch. Not to interupt this thread prop rpm is of great intrest.
 

HT32BSX115

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To find tip speed, you need to know (prop) RPM, and circumference (pitch doesn't matter)

With a 15" (1.25' dia) prop, you would have a circumference of [Pi] times D[diameter] or 3.1416 x 1.25' = 3.93 (feet)...........roughly 4ft.............

@ 5600 RPM is approx 93 revolutions per second................ (5600 divided by 60 )

THEN divide by the drive ratio (1.66) ======> 3373 prop RPM or approx 56 prop revs per sec

The tip of one blade would travel approx 4ft (the circumference) every revolution

Since the blades make a "round-trip" 56 times per second, the tip speed is approx 56 times 4' or approx 220 ft/sec

[there's also the speed through the water which would make the actual speed and direction (vector) of the prop tip through the water not exactly in a perfect circle......)


Now the real question is what RPM, speed, blade angle and load produces cavitation. That requires you to know a few more "things" like blade area, number of blades, viscosity of the liquid, diameter, RPM, and a whole lotta math! yada yada yada!


I found some info on cavitation of marine propellers including one that was written by some guy for his PHD dissertation!! (OMG!!)



I'm gonna have to defer to Bruce on that stuff!! I'm only an EE from 1978. I'm great with Ohms and Kirchoffs Laws........but not all that great with Computational Fluid Dynamics!
 
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alldodge

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Do you know the math to figure out my blade tip speed..1.66@5600 20 pitch. Not to interupt this thread prop rpm is of great intrest.

I see no interruption of this thread, I like seeing what is being discussed as part of what I'm trying to figure out, so continue on please
 

Tail_Gunner

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To find tip speed, you need to know (prop) RPM, and circumference (pitch doesn't matter)

With a 15" (1.25' dia) prop, you would have a circumference of [Pi] times D[diameter] or 3.1416 x 1.25' = 3.93 (feet)...........roughly 4ft.............

@ 5600 RPM is approx 93 revolutions per second................ (5600 divided by 60 )

THEN divide by the drive ratio (1.66) ======> 3373 prop RPM or approx 56 prop revs per sec

The tip of one blade would travel approx 4ft (the circumference) every revolution

Since the blades make a "round-trip" 56 times per second, the tip speed is approx 56 times 4' or approx 220 ft/sec

[there's also the speed through the water which would make the actual speed and direction (vector) of the prop tip through the water not exactly in a perfect circle......)


Now the real question is what RPM, speed, blade angle and load produces cavitation. That requires you to know a few more "things" like blade area, number of blades, viscosity of the liquid, diameter, RPM, and a whole lotta math! yada yada yada!


I found some info on cavitation of marine propellers including one that was written by some guy for his PHD dissertation!! (OMG!!)



I'm gonna have to defer to Bruce on that stuff!! I'm only an EE from 1978. I'm great with Ohms and Kirchoffs Laws........but not all that great with Computational Fluid Dynamics!


You and my son would get along quite well, he takes a certain delight in using equation's to solve complex issue's. One of his last course's was in Fluid Dynamic's i tired to get him to help me with a lift pad and he just rolled his eye's and had no time for it. I know airplane props experience bad things when the tip speed goes supersonic but sound travel's much faster in water so..what ever its annoying.
 

alldodge

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I'm hopping aboard for this one. :) Great work so far AD!

Thanks and good to see you.

Currently looking for the best way to heat my 30x48x16 pole barn so I can get some work done. Very bored but hate the cold
 

Scott Danforth

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build a woodburning stove. you should be able to heat the pole shed easily. build one that will fit pallets in it. most businesses give pallets away for free.
 

HT32BSX115

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Thanks and good to see you.

Currently looking for the best way to heat my 30x48x16 pole barn so I can get some work done. Very bored but hate the cold

I put one of these (below) on my shop. My neighbors bring me used oil to run it!!

This one is new ...... I got mine used from craigslist for about $500 and had to spend another $500
to get it to proper running condx! Now, 1gallon of any kind of oil, diesel, kerosene, solvent etc gives me 1 hour of heat!!
NO gasoline, lacquer thinner, or other mineral spirit that has an ignitable vapor though (can you say BOOM?)
9963.jpg
 

Scott Danforth

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the shops at Cummins were heated with those. they do throw off the heat.
 

alldodge

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I have an old home house wood burner with a blower, one which looks like a regular furnace, but don't know what insurance would say if I install. Looked at the propane models and like them but don't much like the cost of running them. The oil burners I really like but the up front cost is usually high. I'll look into the one shown above. Each year I guess I recycle 40 gallons of oil, with all the stuff I have to change. Have a brother in law with a big rig and he can supply me with all I want but would have to drive to IN, probably worth it. Will look into the cost

Thanks
 

HT32BSX115

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I have an old home house wood burner with a blower, one which looks like a regular furnace, but don't know what insurance would say if I install. Looked at the propane models and like them but don't much like the cost of running them. The oil burners I really like but the up front cost is usually high. I'll look into the one shown above. Each year I guess I recycle 40 gallons of oil, with all the stuff I have to change. Have a brother in law with a big rig and he can supply me with all I want but would have to drive to IN, probably worth it. Will look into the cost

Thanks

I don't think it would be all that great to buy one at retail, but if you consider what you'd pay for an HVAC guy to install a regular forced air furnace, the upfront cost for the Lanair isn't all that bad considering that you'd essentially be running it on free fuel if you had a supply of it.

I got mine from Craigslist and every so often, I see them for sale..... The guy put it there for $1500. When I looked at it, the burner was disassembled. They couldn't figure out why it didn't work right.

I offered $500 because it was taken apart and he said "get it out of here!!"

Turns out they had the fuel filter in upside-down so the nozzel would plug almost immediately!! Only took me a min to fix it!! SCORE!
 

alldodge

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Spent a couple hours with Eddie yesterday discussing my engine and seeing all the major HP he is currently working on, and there is some serious HP in the building. Plan is to bore and basically replace all moving parts except valves and crank. Good thing I replaced the valves some years back with Inconel or they would probably go as well. Going to cut down the runners on the intake, open up No 7 injector, do custom fuel rail work, change to cool fuel, and change over to a MEFI-3 ECM. Compression will be held down a bit so I can run 89 octane instead of 93 so this impacts the amount of HP produced. Would sure like to keep my silent choice but I need to get the risers up another 3 inches, and EMI doesn't make +3 risers to work with silent choice. So just bought +3 risers and will remove my Y-pipe. If it turns out it bothers me to much with my Corsa mufflers, may look into others later.
 

Scott Danforth

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you could go with custom S-pipes to use the silent choice.

When I worked at Champ, we used to make all of EMI's heat exchangers
 
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