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Old 03-15-2015, 04:48 PM   #1
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Default 3000SCR Difficult to Plane

When I say difficult I mean all conditions must be met. I have twin carbed 4.3s with alphas, and a gen set. That makes for an underpowered heavy boat. With a clean bottom, full fuel, full water, gear and three passengers, she will get up if you know how to dance with her, as in throttle, trim tab, everybody lean forward etc etc. then she will run full out 26-28 knots and cruise at 20-22.

As the bottom collects marine growth, you have to make adjustments, less water, less fuel, less people. It can be done with full weight but the dance is much harder. Obviously the answer is scrub the bottom more, but my question is; has anybody fitted a 4 blade prop to combat this? My fear is that I will lose cruising speed and it may over stress the old Alphas.

Ideas, thanks.
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Old 03-15-2015, 05:41 PM   #2
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First what is the WOT for the boat?

Props in good shape?

Adding blade area (4 blades) increases load on the engines so pitch will need to be reduced.

Go to mercs prop calculator and see what it suggests.

Have you assessed the health of the engines? Compression, timing advance working,...
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Old 03-18-2015, 12:02 AM   #3
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I have a 1995 2400 SCR Bravo 2 Mercruiser 350 Horizon power. It is kept on an Air Dock boat lift so the bottom and drive are always clean. I cruise 30 mph at 3500 rpm and top speed of 46 at 5100 rpm. Get a boat lift and everything will change. Get those drives out of the water asap.
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Old 03-18-2015, 12:24 AM   #4
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Apples and Oranges Calguy.

OP, call these guys. They worked wonders for a buddy that had a pig of a 2800.

Hill Marine - Stainless Steel Boat Props & Accessories


It's worth a call.
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Old 03-18-2015, 12:46 AM   #5
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Phillbo...... the point is.. none of these boats with 1 or 2 stern drives were never meant to be kept in the water full time....especially salt water. You want this guy to spend over 2K for new props?? It is a short term fix. I am still using my original 1995 Mercruiser props because the boat has been kept out of the water for since new. The top performance of of every boat depends on the cleanest hull and outdrives........
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Old 03-18-2015, 01:58 PM   #6
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Sounds to me like he has an issue that can be addressed even with a clean hull. I was just passing on advice.
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Old 03-24-2015, 12:11 AM   #7
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Thank you all for the great responses. Although my boat is almost 20 years old (I'm the second owner) it has very low hours. My engines are healthy as in they run very smooth and don't smoke, I spent quite a lot last year on new risers and manifolds due to inactivity from the previous owner. I don't think I'm getting all the WOT I should be, both engines seem to top out at a little over 4.5 k rpm, I haven't been out to check yet this spring. Last summer with a fresh bottom, she pulled 29 knots (gps registered) with just the Bimini top and low fuel load. I normal cruise at 22-24 knots , my memory is a little foggy.
I suspect the 4.3 V6 is just not powerful enough with the weight of a gen set, water heater, full fuel and water tanks to pick up a heavy boat like the SCR.

I would love to be able to pick her up, but I don't have a trailer or a truck that could pull it if I did. I keep her in a U.S. Navy MWR Marina on the Potomac River. That means I cannot modify the docks at all, so no floats or cradles. The best I can do is put her on the hard for winter. During the summer, I anchor at a sandy spot in about 4 feet and scrub the growth by hand.

My props are the stock aluminum but I had them rebuilt last summer.
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Old 03-24-2015, 12:34 AM   #8
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WOT should be around 4600 so you are very close, dropping one pitch will increase it by around 250 rpm.

I think you what you have for this size boat with that power package.
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Old 03-24-2015, 03:31 AM   #9
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Check for water in your bilge, you might be carrying some extra weight there.
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Old 03-25-2015, 01:29 AM   #10
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The bilge in the engine room is dry but I suspect there may be some forward, is there an inspection plate in the cabin?
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