prop question not a lot of info available

[MassManiac]

hello i have a 1989 larson dc-190 cuddy 19ft with a 175 hp 4.3 mercruiser engine and alpha outdrive the boat weighs 2485lbs

my currrent prop is a michagin wheel 4 blade aluminum the numbers are unreadable so i dont know the size or pitch as it got beat to hell when it got grounded

i achieved 40 mph with a load of 500lbs 37mph with 1100lbs at 5500 rpm if my tach was correct

ok my question is i would like to find a prop that would get me a lil more speed like around 45mph
thanks i wish i had more info

 

[rrhodes]

Re: prop question not a lot of info available

It would be a crap shoot without knowing what your current prop is or was. Sounds like you were propped right though.

 

[cr2k]

Re: prop question not a lot of info available

Proping a boat is a lot like putting big tires on a compact truck. Too much and you will lug the engine and build carbon, contaminate the oil, etc. Too little and you will over rev the engine and create stress and shorten it's life.

Since you don't know what pitch the original was you should try to take it to a shop that may be able to put it on a pitch block and determine what it is.

You didn't say what RPMs you were at at 40 MPH.

Ideally you should prop the boat to hit Mfg stated RPM limit at WOT with "normal" load i.e. the load of passengers and cargo you use the most.

5500 seems a little on the high side (I think for that engine) so a little more pitch may be OK. Also most prop catalogs offer a chart based on size, weight, and engine.

Altitude is also another consideration since you will lose power at higher elevations you would use a lower pitch prop to compensate.

Sorry I could not be more specific with the info given, but I hope you have an idea of how this works.

CRaig

 

[rrhodes]

Re: prop question not a lot of info available

I stand corrected... I think that engine's Max RPM should be about 4800rpm.

 

[steelespike]

Re: prop question not a lot of info available

Did you check under the nut for numbers.
Just an educated guess try a 21"pitch prop.Check out the Turning point Hustler excellent all around performance.Watch your rpm you need 4,800 as the max.Let us know your rpm with the new prop.
I feel that if anything a healthy engine will over rev a little but you can back off if necessary.If it luggs then you'll need to go to a lower pitch.

 

[MassManiac]

Re: prop question not a lot of info available

cr2k
my prop is too far broken to bring it to a shop,apparently the person using my boat that day hit an underwater stone wall

the rpm's were at 5500 at 40 my tach is off i believe by 1k

been unable to find a catalog that will help me find the right size and pitch which is why i am now here

steele
i cant find any readable numbers the boat was moored in the ocean prior to me buying it last year

a better question might be if someone with a similar setup 4.3 merc 175hp with alpha sterndrive loaded boat wieght 4000lbs runs for a prop (size and pitch) and what speed they get would be nice
thanks for the help

 

[hwsiii]

Re: prop question not a lot of info available

According to my program you were running a 17" Pitch prop at about 4,500 RPM and 40 MPH if you had about a 10% Prop Slip.

H

 

[MikDee]

Re: prop question not a lot of info available

Did you check under the nut for numbers.
Just an educated guess try a 21"pitch prop.Check out the Turning point Hustler excellent all around performance.Watch your rpm you need 4,800 as the max.Let us know your rpm with the new prop.
I feel that if anything a healthy engine will over rev a little but you can back off if necessary.If it luggs then you'll need to go to a lower pitch.

I agree, this prop pitch should be pretty close, and the Turning Point Hustler is one of the best, also at a bargain price here, & now. You may be able to buy it, & exchange here it if the pitch, & rpm , is not right.

 

[MassManiac]

Re: prop question not a lot of info available

found a few reconditioned props at my local marina real cheap a 14X19 and a 14X21 will pick them up next weekend and test them out and post the results

gotta work on the electrical this weekend to figure the tach problem


thx for the help and info once i find the right pitch i want i can look into to getting one of those nice props

 

[hwsiii]

Re: prop question not a lot of info available

Mass I show a 1.65:1 gear ratio for that motor, if that is true you need a 17" prop for that combination. If you had a 21" prop on that boat it should have been doing about 49 MPH at 4,500 RPM. The following are my numbers that reflect that.

Boat and motor

Prop Picker

Prop with 21" Pitch

H

 

[MikDee]

Re: prop question not a lot of info available

found a few reconditioned props at my local marina real cheap a 14X19 and a 14X21 will pick them up next weekend and test them out and post the results

gotta work on the electrical this weekend to figure the tach problem


thx for the help and info once i find the right pitch i want i can look into to getting one of those nice props

Good! After rethinking this, a 21" pitch might be a bit too much? a 19" pitch maybe just right, if your marina will let you, I would try the 19" pitch first, but swap for the 21" P if need be. On that 4.3 V6 I think the specs are to reach 4600rpm Max (check your engine for specs).

By the way, the tach usually has settings on the back, these may be off?

 

[MassManiac]

Re: prop question not a lot of info available

hws where would i find a calculator like that?

a nice stroke of luck yesterday while cleaning out the boats interior i found the boats spare prop i managed to get the numbers and figure out it was a michagin wheel 992404 11" pitch 3blade
it was a bit dinged up on the edges so i cleaned them up and made sure all 3 blades where the same dimensions and took it out this morning

WOT rpm 4600 speed 37 weight boat+passengers/gear 2900lbs on glass

i appreciate all the help guys and im still gonna stick to my plan on buying both 19 and 21 and let you all know the results

thanks again

 

[hwsiii]

Re: prop question not a lot of info available

Mass, that is my personal program I designed and wrote for picking the correct prop for a boat. And I assume you meant a 17" pitch Michigan aluminum prop, not an 11". And it is a waste of time to get the 21" pitch aluminum as you will be turning only 3,800 RPM and lugging that motor baddd.


H