modifying pitch on S/S prop

torcano · Apr 5, 2012

I going to have my SS Avenger props sent out for reconditioning. I only was able to get 4350 RPM at WOT during a recent sea trial. Can the pitch on these props be slightly reduced to achieve a higher RPM at WOT?

Philster · Apr 5, 2012

Re: modifying pitch on S/S prop

Yes.

But... why did you fall short? What props are on there now??

steelespike · Apr 5, 2012

Re: modifying pitch on S/S prop

Agreed Don't make any changes till you tell us the info in "read this first" at the top of the main prop page.

jkust · Apr 5, 2012

Re: modifying pitch on S/S prop

See the youtube videos of how it's done by the shop.

torcano · Apr 5, 2012

Re: modifying pitch on S/S prop

Here is what I have.
Mercruiser Avenger SS props
Pitch 17, not sure on diameter I think they are 15 inch diameter counter rotating
WOT RPM 4500
Twin 4.3 Mercruisers MPI
2002 SeaRay 280 Sundancer weight 8000lbs

steelespike · Apr 5, 2012

Re: modifying pitch on S/S prop

Do you have the speed indicated at 4350? Is it by gps?Was the boat sluggish in general.

torcano · Apr 5, 2012

Re: modifying pitch on S/S prop

GPS was not working. Surveyor estimated speed at 32 knots at 4350 RPM. The RPM was taken from the engine via a computer that was plugged in to the engine. The boat did not seem especially sluggish. The hull was power washed prior to the trial but I would say the drives were only 95% free of growth.

Philster · Apr 6, 2012

Re: modifying pitch on S/S prop

I'd want more RPM, too.

Here are the variables that would make me pause before proceeding:

What prop did she wear out of the factory?

Were they 17P? If the answer is 'YES', then the health of the engines is suspect as is the condition of the boat's hull/structure.

So... you can go through the basic from tune ups all the way to compression or leakdown tests.

As for the hull, you have to be very careful, as it is my understanding that Sea Rays are fully cored with balsa wood. Improper care and slapping on stuff over the years can lead to water intrusion into the core and a heavier boat. It's usually just enough weight to knock the RPM down to just below the acceptable range. When the engines run like this, they are under severe stress and risk internal failure or premature wear.

If the boat is simply wearing the wrong props because the owner changed them to a bigger pitch/diameter/style/whatever, then you can put lower pitch props or smaller props and get the RPM up.

You just don't want to put smaller prop on her to cover up a loss of power from the engine(s) or because she has a wet core.

steelespike · Apr 6, 2012

Re: modifying pitch on S/S prop

Unfortunately estimated speed is too vague. According to the info your running about 25% slip.
I'm more inclined to think that number is at least partially from incorrect speed even though a heavy boat will produce higher slip
numbers.My info indicates 4800 max rated rpm and 15" pitch should give about 4750.15 does seem pretty low.
As Philster suggests be sure other influences are in order.

nlain · Apr 6, 2012

Re: modifying pitch on S/S prop

Specs from SeaRay site, looking at the site I think these specs are with the 496 mag B III 375hp engine, (standard power) you have T-220hp 4.3L B III. You should be able to take this info along with the fuel, water, holding tank and other stuff on the boat and get close to actual weight. Then, if you have a trailer, go get it weighed and see how close you are.

S E A R A Y S P O R T C R U I S E R S 2 0 0 2
2 8 0 S U N D A N C E R
OVERALL LENGTH
W/STD. EXTENDED
SWIM PLATFORM 31' 1" 9.47 M
BEAM 9' 5" 2.87 M
DRAFT
(STERN DRIVE DOWN) 39" 99.1 CM
(STERN DRIVE UP) 22" 55.8 CM
(TWIN STERN DRIVE DOWN) 39" 99.1 CM
(TWIN STERN DRIVE UP) 23" 58.4 CM
DRY WEIGHT 8,000 LBS 3,628.8 KG
FUEL CAPACITY 100 GAL 378.5 L
WATER CAPACITY 28 GAL 106 L
HOLDING TANK 28 GAL 106 L
DEAD RISE 21? 21?

A link to this info: http://www.searay.com/Page.aspx/pmId/16355/pageId/10250/view/Overview/Past-Models.aspx

Philster · Apr 6, 2012

Re: modifying pitch on S/S prop

Your Avenger props are aftermarket props from Michigan Wheel.

They are 14.5 or 15.5" diameter, SS and 3 blades. They are a 'universal' blade design, which is quite vanilla and won't help your boat do any one thing well.

Manufacturer: Michigan Wheel
Brand: Avenger
Material: Stainless Steel
Diameter: 15 - 1/2” or 14 - 1/2"
Pitch: 17”
Blades: 3

The fact that they are aftermarket props introduces a variable.

Philster · Apr 6, 2012

Re: modifying pitch on S/S prop

Also, I would think the surveyor had at least a GPS App on his phone/ipod/whatever.

torcano · Apr 6, 2012

Re: modifying pitch on S/S prop

Thanks for all the information. I thought the props were original to the boat but I am the third owner so I can not say for sure. The engines checked out fine during the sea trial including a leak down test. I thought Searays do not have cored hulls. According to my survey report the hull is a molded FRP solid laminate. The engines are curently getting a full tune up including new plugs, distibutor, rotar, etc. I was thing of getting the props reconditioned and re-testing it. I bought a new Garmin GPS and new tachs so I should be able to assess an acurate speed over water and RPMs at WOT. The boat was serviced on a regular basis so this does not appear to be a negelected boat. Engine hours are only 230. The drives are alpha 1 generation II, not bravos.

Philster · Apr 6, 2012

Re: modifying pitch on S/S prop

Leakdown can't speak to fuel flow or ignition. Tune up: good.

Jeeze, Sea Ray was big into balsa core, but it's possible they switched over to something else by the date of your build. Solid laminate? Gotta look that up.

The props might be dogs. Vanilla design. If they don't lift very well, you might have more wetted hull and that'd easily add enough resistance to hold RPM (and speed) down a bit.

Philster · Apr 6, 2012

Re: modifying pitch on S/S prop

Well, FRP solid laminate might be worse. It might be perfect on your boat, but be advised that removing wood from the core doesn't mean you can ignore it:

http://www.yachtsurvey.com/cored_hull_bottoms.htm

Just informational. Wood ain't the only thing that holds water. There are foams and other core materials that do so, too.

torcano · Apr 6, 2012

Re: modifying pitch on S/S prop

I wish I read that article before I bought a SeaRay but it's too late now. I guess I can just hope for the best at this point. The hull taping and moisture readings all checked out but it looks like these types of problems can evade external dectection. I just bought a in hull transducer for a GPS that states it will not work in a cored hull. Am I correct to assume if my hull is FRP solid laminate it is not cored? I guess I will find out for sure next week when the boat goes back in the water and I install the transducer.

steelespike · Apr 7, 2012

Re: modifying pitch on S/S prop

Not to digress but:: Fiberglass boats have been around since the 1950s.
Some are still operating .I wonder are these older boats just lucky or just better built in the first place?
I've always shied away from fiberglass even though bottoms can be faster and forms more graceful.
Lets face it Aluminum is pretty basic with todays basic shape looking all like clones.
My 57 Crestliner has good lines resembling a wood boat. The Feathercrafts of the 50s looked very stylish.
And I think Caddilac built some wild aluminum designs.
nuff said.back to business.

modifying pitch on S/S prop

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