Dialing it in after repower

[ejones04]

The boat:
1988 Marine Trader Tradewinds 47 Tri Cabin Sun Deck
370 recon Cummins x 2
ZF 220 1.963 :1
26×16 3 blade props
2 1/4 shafts
47ft loa, water line 42ft, beam 14’6, 34,873 lbs as tested.
Fuel: 800 gals capacity…..300 gals est for testing.
Water: 200 gals capacity…….. 50 gals est for testing.
Holding Tank: capacity 50 gal…… 0 gals for testing.
SMX Turbocaters
SMX dbl – dbl with prime bulb
SMX fresh water flush kit
Followed SMX exhaust design to keep turbo dry
SMX 5” low restriction mixer
5” lift muffler with straight 5” run to transom
SMX 160 T Stats
So my first couple of test runs I realized I’m over propped, maximum RPM is 2700 with 20 pounds of boast and a pyro reading of 700. Speed was 16.8 knts at the 2700 RPM, both engines were around 180 degrees, I could back off to 2300 RPM still be on plane at a speed of about 14 1/2 knts, looking at the prop calculator it’s suggesting a 24 x 21 my question is would I be better off staying with a 26 diameter and dropping down to a 16 inch pitch, is a bigger diameter considered better or it makes no difference and if I have to buy new props would a four blade be better than the three blade in my application.

Topic

[Tony Athens]

You really needed 2.5:1 gears for this boat.. Who was guiding you in this project? Big shafts, heavy boat, and trying to stay as efficient as possible all equal slowing turning big props…………………………IMO, someone made a “bad choice” here.

Current Props: Exactly where did there 26 x 16 props come from? Exact make & specs, please

NEXT: Diameter is the key in a boat like yours, but you really need to get the engine RPM up to an accurate 3100-ish..”Flat props” like a 26 x 13-ish will be hard to find in an efficient / modern design. Loosing 2″ in diameter is major………………………………………..

How important is it for you to cruise above “wine & cheese” speeds? Was being able to plane and run 30-60 miles to some destination part of the original plan?

Be accurate here–How loaded was the boat on your seatrial that got the boat up on plane?

[Author]

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