Logo
FULL SITE MENU

which prop?

R

redrider

New member
I have a 1988 sunray bowrider with a 100hp mariner. The prop is getting pretty chewed up and I would like to get a little more performance. The numbers on the prop I have are 402 48 77348 440L 21P and it is aluminum. It goes ok but it really has to dig down deep to get going and I have to work alot on the power trim to get a top speed of about 35 mph. It can barely get a skier up. Is this normal or is there something better out there? The motor also has an aftermarket fin on it ,about 15" wide, for stability I am guessing. Any advice? Thanks, rr.
 
Do you have a tachometer on the boat?

If not we will have to assume that your current 21 pitch prop was "fitted" correctly for your rig.

If the motor is labouring trying to get going that is a fair indication that you have "too much" pitch unless the motor needs a good tune up.

The fin is there to help get the boat up on plane quicker - it places quite a bit of stress on the cavitation plate of the motor and does make it more difficult to steer in turns (which puts added stress on the steering system), but does have some limited usefulness if you travel long distances through canals or no wake zones by keeping the bow down enough that you have good visibility forward).

Contrary to the claims of the mfg's of "fins", they do not add any "noticable" improvement to top speed or fuel economy.

(should have added)

Off the top of my head, a ski style boat in the 17/18 foot range with a 90-115 horse motor would generally run a 17 pitch prop - maybe a 19 if the boat was aluminum and possibly down to a 15 if it a heavy fiberglass build - so unless you have a light 15 footer, 21 sounds quite "high"...

It sounds like a previous owner was trying to address a "percieved" sub-standard performance from the rig. Which means that you could be "over propped" as well.

There is a myth out there that "More Pitch = More Speed" - that is only true if you were running way too little pitch in the first place - otherwise, more pitch just causes the motor to bog and can do significant damage to the engine.

So before we can really advise on a prop, need a couple pieces of information -

does the boat have a tachometer? if so, what rpms do you get at full throttle?

(if not)

what is the max recommended horsepower for the boat? (look for the coast guard plate)

if you can't find that - what is the length of the boat? what model? (ie sunray 220 or whatever)

Without a tach, which is really the only way to properly determine "what prop" should go on "your" boat (identical boats with the same motor will run different props, there is no "one size fits all"), we will have to try and figure out what you should "maybe" be running in general...
 
Last edited:
Sorry, I forgot to mention the boat is a Sunray Express, 17.5'. There is no tach on the boat. The US coast guard plate recommends a 105 hp motor and a 6 passenger 945 lb weight limit and the Canadian coast guard plate recommends 84 kg motor limit. ( 112 hp, app) We usually run with 2 or 3 *****s in a good sized lake where we can go at a good clip most of the time. thanks for your input.
 
Sounds like you have enough motor but too much prop - I really think that a 17 pitch would be more in line with the boat, how you load it and use it.

Looks like your boat tips the scales at a touch over 2000 lbs (dry), plus 350 lbs of motor, plus gas, battery, safety stuff, junk for the day and your "crew" - another 600 pounds (on the conservative side) - so a "rigged weight" of about 3000 lbs.

That being pushed by a 100 horse - ok - but not with 21 pitch - that's too much (I can sometimes run a 19p on my 140 which is pushing about 2800 lbs rigged/loaded but I most often run a 4 blade 17p which better handles the weight in the hot/humid weather which can suck 10-15% of your motors power).

If you find a decent place that sells props they will often have a "shop tach" - maybe they can help you out...
 
Last edited:
Back
Top