Improving Planing Performance with Four- or Five-Blade Propeller

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Author Topic:   Improving Planing Performance with Four- or Five-Blade Propeller

yarmul posted 09-30-2009 03:12 PM ET (US)
I have a 1999 [SeaRay] 215 express cruiser with a 5.7 liter[MerCruiser] engine with 150 hours on it. It has a [ALPHA 1 sterndrive] with a three-blade 15 right-hand propeller. I run it between 5,300-feet and 3,200 feet in elevation. At full throtle slightly trimmed up I can run 39- to 41-MPH at 4,800-RPM. I just installed a swim platform on at the start of the summer and the extra 200-lbs right over the sterndrive has slightly affected the performance of how fast I can plane over. If I have six adults on the boat I can't even plane over. With two or three adults and two kids I'm okay. If I change the prop to a four-blade or five-blade will this help me getting to plane? Once I'm on plane I'm fine. Please let me know options.
Thanks
Tom W Clark posted 09-30-2009 10:03 PM ET (US)
There is far more to propping a boat than simply choosing how many blades the propeller has.
You'll need to tell us what propeller you are using now, what the gear ratio of your outdrive is and what the recommended WOT RPM range of your motor is, for starters.
kwik_wurk posted 10-01-2009 01:17 AM ET (US)
Do you have trim tabs on your boat, if not you need them. (And trim them down all the way when you start, and then start backing off once you're up.)
With six adults you added maybe 1000 lbs. And your dry wieght is 3800, so loaded with fuel, gear, and 6 persons you're ~4500 lbs.
You should get up on a plane eventually with the prop you have based on current performance you have given...
You could have a rough running engine and not know it. I have the same engine and aplha drive and found this out. I had 8 people in the boat and barely planed. The next day I went through the plugs and found one that was gummed up. (Replaced it, and had the 8 people in the boat, and just fine.)

And yes we need your prop info.
Tom - 5.7L typically are rated between 4400-4800 (250 hp). Alpha 1 typically are 1.62 reductions. So prop shaft speed is 2,962 RPM.
(And I assume he does not have an EFI, because it was not stated.)
Lil Whaler Lover posted 10-01-2009 07:01 AM ET (US)
Can't assume the gear ratio if the boat is used at altitude. Mercury would usually ship a non standard gear ratio to help compensate for the altitude. Ran into this once in Maine with a boat a customer brought to sea level from high altitude.
The gear ratio should be right on the lower unit.
yarmul posted 10-01-2009 10:15 AM ET (US)
I have 1:62 gear ratio and a ballastic 15 degree 3 blade prop. My WTO is 39-40 mph at 4800 rpm. I do have trim tabs I don't use them all that often and when I'm pulling a wakeboarder out of the water its kind of a pain to use them.
yarmul posted 10-01-2009 10:16 AM ET (US)
Yes I do have EFI. I had the original plugs changed yesterday and they didn't look all that bad.
Tom W Clark posted 10-01-2009 12:10 PM ET (US)
Well, on the face of it you are not doing too badly. 39.5 MPH @ 4800 RPM with what I assume is a Michigan 14-7/8" x 15" Ballistic three blade, Michigan (part # 345131) propeller is about 6 percent propeller slip.
That may not be the ideal propeller. You might benefit form a prop with more blade area. Three propellers you might try are:
15-3/4" x 15" Mercury MIRAGEplus
14-5/8" x 15" Mercury Revolution 4
14-3/4" x 16" Mercury Enertia
If your chief objection is not being able to get on plane, you might try a prop with vent holes. The Mercury props all use their PVS system which allows you to vary the size of the venting which will allow your motor to spin up to a part of power curve that may get you on plane.
The use of trim tabs will also get you on plane when heavily loaded.

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Author	Topic: Improving Planing Performance with Four- or Five-Blade Propeller
yarmul	posted 09-30-2009 03:12 PM ET (US) I have a 1999 [SeaRay] 215 express cruiser with a 5.7 liter[MerCruiser] engine with 150 hours on it. It has a [ALPHA 1 sterndrive] with a three-blade 15 right-hand propeller. I run it between 5,300-feet and 3,200 feet in elevation. At full throtle slightly trimmed up I can run 39- to 41-MPH at 4,800-RPM. I just installed a swim platform on at the start of the summer and the extra 200-lbs right over the sterndrive has slightly affected the performance of how fast I can plane over. If I have six adults on the boat I can't even plane over. With two or three adults and two kids I'm okay. If I change the prop to a four-blade or five-blade will this help me getting to plane? Once I'm on plane I'm fine. Please let me know options. Thanks
Tom W Clark	posted 09-30-2009 10:03 PM ET (US) There is far more to propping a boat than simply choosing how many blades the propeller has. You'll need to tell us what propeller you are using now, what the gear ratio of your outdrive is and what the recommended WOT RPM range of your motor is, for starters.
kwik_wurk	posted 10-01-2009 01:17 AM ET (US) Do you have trim tabs on your boat, if not you need them. (And trim them down all the way when you start, and then start backing off once you're up.) With six adults you added maybe 1000 lbs. And your dry wieght is 3800, so loaded with fuel, gear, and 6 persons you're ~4500 lbs. You should get up on a plane eventually with the prop you have based on current performance you have given... You could have a rough running engine and not know it. I have the same engine and aplha drive and found this out. I had 8 people in the boat and barely planed. The next day I went through the plugs and found one that was gummed up. (Replaced it, and had the 8 people in the boat, and just fine.) And yes we need your prop info. Tom - 5.7L typically are rated between 4400-4800 (250 hp). Alpha 1 typically are 1.62 reductions. So prop shaft speed is 2,962 RPM. (And I assume he does not have an EFI, because it was not stated.)
Lil Whaler Lover	posted 10-01-2009 07:01 AM ET (US) Can't assume the gear ratio if the boat is used at altitude. Mercury would usually ship a non standard gear ratio to help compensate for the altitude. Ran into this once in Maine with a boat a customer brought to sea level from high altitude. The gear ratio should be right on the lower unit.
yarmul	posted 10-01-2009 10:15 AM ET (US) I have 1:62 gear ratio and a ballastic 15 degree 3 blade prop. My WTO is 39-40 mph at 4800 rpm. I do have trim tabs I don't use them all that often and when I'm pulling a wakeboarder out of the water its kind of a pain to use them.
yarmul	posted 10-01-2009 10:16 AM ET (US) Yes I do have EFI. I had the original plugs changed yesterday and they didn't look all that bad.
Tom W Clark	posted 10-01-2009 12:10 PM ET (US) Well, on the face of it you are not doing too badly. 39.5 MPH @ 4800 RPM with what I assume is a Michigan 14-7/8" x 15" Ballistic three blade, Michigan (part # 345131) propeller is about 6 percent propeller slip. That may not be the ideal propeller. You might benefit form a prop with more blade area. Three propellers you might try are: 15-3/4" x 15" Mercury MIRAGEplus 14-5/8" x 15" Mercury Revolution 4 14-3/4" x 16" Mercury Enertia If your chief objection is not being able to get on plane, you might try a prop with vent holes. The Mercury props all use their PVS system which allows you to vary the size of the venting which will allow your motor to spin up to a part of power curve that may get you on plane. The use of trim tabs will also get you on plane when heavily loaded.