Looking for a engine hoist to raisesome outboard engines. After changing the props for the fouth time. I am now trying to do anything that will help in top end speed increase while maintaining good RPM through out the running range. After much research on props. I feel that if a raise the engines one slot and maybe increase the pitch 1 degree I will get the extra 3 to 4 knots I am looking for without killing the WOTRPM very much.If any one has any advice on props selection and other thing to do, to get the extra speed please advise. I now run 30 knots at 4500 rpm with 5 guys 200# ice and 250 gallons of fuel If we increase fuel to 300 gallons I will lose 3 knots. WOT now is 5600 no trim and loaded, around 41 knots max. Thanks for any help. Gene
Looking for a loaner engine hoist
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Gene you may not have to raise that engine. What are the size and number of blades you are using now? First go tothe belowsite and figure your slippage. then when you have that slippage figure give me a call and I may be able to help you.
http://www.rbbi.com/folders/prop/propcalc.htm
Ron 850-712-2603
http://www.rbbi.com/folders/prop/propcalc.htm
Ron 850-712-2603
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If you guy's can/would, I would like to see what you come up with. I'm running the same motors, and would like to see if I'm running effeciently.
My dry wieght is 8,000lbs. For reference I was doing 39-40mph (GPS) going past Gene @ 4700rpm's. 650 lbs of crew, 70gal of gas, 40lbs of fish, 150lbs of ice.
My dry wieght is 8,000lbs. For reference I was doing 39-40mph (GPS) going past Gene @ 4700rpm's. 650 lbs of crew, 70gal of gas, 40lbs of fish, 150lbs of ice.
Scot I don't feel so bad now. I was running 30 knots about 33mph at 4500 rpm's 3 big guys and 2 smaller ones 175 gallons of fuel and a cooler of fish. I think and hope that I can push the cruise speed up 3 to 5 knots, by increasing the pitch 1 degree and raising the engines one slot and also increasing the RPM's to 4700. I am going to Sherman in the morning and start testing again. I let you know what I find out. Gene
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Gene if you increase the pitch your RPMs are going down and you will be loading the engine more. You are in the ball park for correct % of slip with your calculations book says 10 to 20% and you are at 16.5%. What is your gear ratio? last have you called Contender and asked them. Accu prop would be another place to ask, Take you props to make sure they are correct.
Ron
Ron
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Thanks Gene,
Forgot to put upprop info.3 Blade Stainless Mercury Mirage 19P. Not sure of the diameter.
When I tried your 4 blades, (thanks for that) I ran 500-700 rpm higher and ran 5-10knts slower. I did "power" through the rougher seas better, and jumped up on plane faster.
I felt with your props that the motors were working to hard for the performance.
On the rig trip,with the 3 bladed props, the boat ran better at higher rpm, and speed (4100-4200) in 2 to occasional 3. It seemed we did not get beat up as much. Maybe jjam or Ocean Man could say what they thought.
Scot the props I loaned you were off the Hydra-Sports 2650.19 pitch 4 blade. I bought a set of 18 Pitch 4 blade power tec from accu prop about six months ago.
Ron Contender says that the new 4 stokes are alot more heavy then the 250 yamaha os66 that came off the boat org. Some of the older model like mind had a porpoise problem with the extra weight. They recommended wedges, which Ialready hadinstall with the four storkes. They also recommended raising the engines up one to two slots. I raise the engines up one slot about three months ago with no increase in speed or difference in RPM's.Boat ride also the same. I still plan on raising another slot and hope the rpm and slip does not go up. Maybe with a little less drag is were I hope to get the extra speed.If everything stays the same at that point I will eat the 200 RPM decrease with hopes for a little more speen at cruise. Thanks for your help the charts you sent were very helpfull. Gene
Ron, Tim and I did another test on the boat this morning. Here is what we found. With 150 gallons of fuel,2 person and no gear. WOT 5975 wow,engines trimed up, half trim on tabs, speed was 41.8 knots,no porpise. With the chart you sent me I had less then .09 slip.By the way my gear ratio is 2.0. With my new readings I feel that 1 degree pitch change will do it. What do you think? Genesealark (1/29/2010)OK Gene, I see your problem Now... 4 strokes... Can you tell I might be a little predujice. Go E-tec.![]()
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Gene, with the new figures your slippage is 17.9%. To get that from the Decimal in the calculator just move the decimal point over 2 spaces to the right. Adding an inch to the pitch would allow you to reduce rpm to maintain speed but would load the engine not dangerously but would load it more. Rather than chainging the pitch just increase the RPMs a little. What I do when I get underway with my trim is when I get up and on course I trim up until I start to cavitate ever so slightly and then trim down just enough to not cavitate. If you are trimmed down too far just watch your speodometer and trim up and the speed will start to clime until you start cavitating. That spot just befor cavitation is the most economical place to be. However when sea states change or swells are encountered the trim might have to be adjusted.
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