Which Props will work best?

[moosehunter74]

I just replaced my old 305 with a new 350 create engine in my boat. I took it out for a couple crabbing trips and did test runs with different props. I tried my old set of 24 pitch Bravo 3 and hit 43.5 mpr @ 5200 rpm's with full tank and 2 adults on board. The other test was with 26 pitch Bravo 3 and hit 46 mpr @ 5100 rpm's with full tank and 4 adults. Should I be going to 28 pitch props or try the XR Bravo 3 27 pitch? I want to achieve best cruising and economy.
Cruise at 30 mpr @ 3850 with 24's
Cruise at 30 mpr @ 3700 with 26's

 

[alldodge]

I think you said you have a boat problem but all I see is

I took it out for a couple crabbing trips and did test runs to bring back some crabs for my iboat friend AllDodge

PM me for my address

Turning 5200 for your 350 is to high, the 350 should be 4600-5000 for MPI MAG horizon. My guess is you do want to first get a hand held tachometer, something doesn't add up. If your boat is not a horizon or been balanced to achieve the rpm your tach is probably off. What do you have and what has been changed

 

[moosehunter74]

I purchased a GM crate motor 350 HO 2 barrel Carb

 

[alldodge]

OK, have many questions:
Is this the auto version which shows 350 hp at 5500 rpm?
What is your outdrive ratio?

Currently still think your tach is off because your slip is way high

 

[moosehunter74]

Yes its the auto version and I think its rated at 333 @ 5100. I have the Bravo 3 @.2.2

 

[alldodge]

Cruise at 30 mph @ 3850 with 24 pitch = 24.57 slip
Cruise at 30 mph @ 3700 with 26 pitch = 27.55 slip
WOT at 43.5 mph @ 5200 with 24 pitch = 19.02 slip

Guess my next question would be, are your speeds taken from a GPS or the boat speed-o?

 

[moosehunter74]

Those where taken from my chart plotter

 

[alldodge]

Those where taken from my chart plotter

Sounds like your speed is accurate, now I'm back to the tach.

What kind of boat is this?

 

[moosehunter74]

No Title

Its a bayliner 2159

 

[alldodge]

That helps, showing the 2160 is from 1986 to 1988, and the boat at 3800 pounds is a light boat. Your slip numbers are way high for that style boat. Now there is a possibility that the hull over time has taken on water and may be heavier.

The issue with the XR prop (4x3) and the 4x4 is as the prop moves forward it will also lift the stern up more then the 3x3. The hull can also cause many issues and I for one know first hand about slip and a single engine cruiser. (have a long story with own cruiser on same issue, currently still working)

The issue that is catching my attention more then any is the slip is so high at cruse speeds. Do you remember any numbers speed/rpm from the boat with the 5.0 ?

 

[moosehunter74]

If i remember i cruised at 3700 rpm's @ 27-28 with 24 pitch prop

 

[moosehunter74]

It's a 2159 and 1993

 

[alldodge]

I find the 2159 remains at the 3450 dry weight, so where a bit lighter but still about the same spot

Old
Cruise at 28 mph @3700 with 24 pitch = 26.75 slip
New
Cruise at 30 mph @ 3700 with 26 pitch = 27.55 slip

Your almost at the same spot as me but I am doing better, I'm in the 23 slip area with a 27 footer. Your putting more power and as you apply more power your slip is increasing.

Instead of the tach I would look more at the hull and if it has taken on water. How hard would it be to take the boat to a truck scale and have it weighted?

 

[moosehunter74]

Not hard at all. Should i weigh it with a full tank? I tested the 26 pitch twice.5100 @ 46 mpr with 2 adults and another time with 4 adults and hit 4950 @ 44 mpr

 

[alldodge]

I would estimate 3450 plus 52 gallons gas @ 6 lbs = 312, plus 500 in gear = 4260 give or take. If you approach 5000 you got a lot of tools or water somewhere.

Just my guess

 

[moosehunter74]

I think its 70 gallon tank plus water and gear and usually take 3 on boat for weekend. I'm just wondering if i should go to a 28 pitch prop. I think i will have enought power to turn them

 

[alldodge]

Your previous numbers with the 26 pitch shows your around 150 rpm below when you had the 24 pitch on. Reducing the 24 pitch WOT by 150 rpm for the 26 pitch would put you in the 5050 rpm range. Going to 28 pitch should move your down to the 4850 or 4900 range.

You will have enough power to turn them but your slip is increasing. you could turn a 30 pitch prop, but your fuel consumption will go up and your hole shot will reduce. I'm just trying to find out what is causing the excessive prop slip.

I'll stick in the area of if the boat is around the 5K range you have water in the hull. Figure the trailer would weight around 1200