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Aquamatic propeller Question

I

Indy1K

Contributing Member
I have a 1986 Sun Runner 310SB cruiser which weighs in at 9,960lbs. It has a waterline length of approximately 28ft and a beam of 11ft 6in.
Original power units(2) are Volvo Penta AQ260/290A I have rebuilt as new original AQ290A outdrives on the boat
This boat will be completely re-powered this year with remanufactured early version(1985) Chevy small blocks from Advanced Engine.

My question is what diameter and pitch props would work best for the boat. When I got the boat, it had 2 15 x 19 aluminum props on it. Because of their condition and the fact that the boat would not get on plane, RPMs would only get up to 3000, I put 15 X 17s on it. It still ran like crap even after going through everything you guys recommended. We replaced the Starboard engine last August, and the boat was running great. got on plane and cruising at about 24-25mph WOT. The starboard(new) engine WOT at 4000rpm, the port engine about 3200 to 3400. So I backed the starboard engine down to match the port engine. Coming back one evening, we threw a rod in the port engine. Ok, tired original 1985 engine. So we are pulling the boat in early April to replace the port engine to match it's brother on the Starboard side.

Looking up prop sizes using the calculator, it says I should run a 17.9 X 20 something. First, I dont know if the diameter of anything bigger than 15" will fit and not hit and second, I think the pitch would be too high and cause slippage. I am thinking of just ordering new 15 X 19s for it.

Any input is always appreciated.

regards,

Kevin and Tatyana
aboard the Russian Princess on the Ohio River
 
Indy1K said:
I have a 1986 Sun Runner 310SB cruiser which weighs in at 9,960lbs. It has a waterline length of approximately 28ft and a beam of 11ft 6in.
Original power units(2) are Volvo Penta AQ260/290A I have rebuilt as new original AQ290A outdrives on the boat
This boat will be completely re-powered this year with remanufactured early version(1985) Chevy small blocks from Advanced Engine.
Suggestion:
DO NOT allow the rebuilder to use the GM Full dished pistons in this build! There are better options for a true marine build that will offer a quench effect!

My question is what diameter and pitch props would work best for the boat. When I got the boat, it had 2 15 x 19 aluminum props on it. Because of their condition and the fact that the boat would not get on plane, RPMs would only get up to 3000, I put 15 X 17s on it. It still ran like crap even after going through everything you guys recommended. We replaced the Starboard engine last August, and the boat was running great. got on plane and cruising at about 24-25mph WOT. The starboard(new) engine WOT at 4000rpm, the port engine about 3200 to 3400. So I backed the starboard engine down to match the port engine. Coming back one evening, we threw a rod in the port engine. Ok, tired original 1985 engine. So we are pulling the boat in early April to replace the port engine to match it's brother on the Starboard side.

Looking up prop sizes using the calculator, it says I should run a 17.9 X 20 something. First, I dont know if the diameter of anything bigger than 15" will fit and not hit and second, I think the pitch would be too high and cause slippage. I am thinking of just ordering new 15 X 19s for it.

Any input is always appreciated.

regards,

Kevin and Tatyana
aboard the Russian Princess on the Ohio River
Click to expand...

Propeller selection is almost always a trial and error ordeal.
Your goal will be to reach the OEM WOT RPM.
Keep trying props until this can be achieved.

I own a 28 foot 10' 4" beam SND F/B boat.
It weighs close to the same as yours.
I have twin Q/E built 5.7s in it with the Duo Prop drives.
I run B-5s on it.

Prior to this, I had s/p drives.
With the s/p drives, it was a slug.

The addition of Duo Prop lower gear units is your answer to much better performance.
Expensive.... yes, but you will not regret it.

 
To recap... 15x19 only let you get to 3000 RPM
15x17 lets you get to 4000 RPM

The correct prop is one that lets the engines, with normal load onboard and a full tank to get to within the maximum Wide Open Throttle RPM specified for your particular engine. I'd look up, on the Volvo site, what the WOT MAX RPM range is for that engine. It's likely in the 4000-4400 RPM range.

That said... It appears as if the previous owner of your boat, dissatisfied with the maximum speed of his boat, increased the prop pitch to 19 which caused the engine speed and boat speed to actually drop... then he sold the boat. This is a common phenomenon with what I call "boat show specials", i.e. a boat with the smallest (and cheapest) engine that will work in order to have a low sticker price.

The 17 pitch prop is just at the bottom end of the rev range. You might want to consider Ricardo's suggestion as to DupProps. The "cheap" fix would be to try 15x15 props. Your boat will not likely go any faster but the engines will be happier.
 
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