Prop Slip

[FreeBeeTony]

Re: Prop Slip

Don't know why you say the Alpha's don't come in 1.5:1 ratio's........maybe because the new ratio's are 1.47:1........??

I am very familiar with Bondo, as he is with me.

the 1.65(2):1 is for the IL6 and some V6 , 1.84:1 for 4 cyl engines and so on.........

http://www.mercurymarine.com/engines/inboards/sterndrives/alphaone_specs.php

 

[Tail_Gunner]

Re: Prop Slip

Don't know why you say the Alpha's don't come in 1.5:1 ratio's........maybe because the new ratio's are 1.47:1........??

I am very familiar with Bondo, as he is with me.

the 1.65(2):1 is for the IL6 and some V6 , 1.84:1 for 4 cyl engines and so on.........

http://www.mercurymarine.com/engines/inboards/sterndrives/alphaone_specs.php

Sorry Tony i can some times ask a question and it turn's out adversarial....That 24 foot boat is a real chunky bugger. It must handle 3-5' rollers quite well. It would be intresting to listen to a desinger and the reasoning for such short gears in a boat like that. What had me going was a 24' Rinell cuddy that i have been looking at.....With a 350 mag and 1.66 gearing she will do 50+ and its 4000 lbs also..

http://madmariner.com/vessels/power_reviews/story/GRADY-WHITE_OFFSHORE_24_082908_VP

As stated above the boat seems to hit the wall @ 34mph..... I guess if it were mine id be chasing some way to get that hull out of the water but i dont believe they make a prop that can lift that bow up and out....Ill bet she just mashes 3-4 footer's....Does it take heavy schocks well???

 

[FreeBeeTony]

Re: Prop Slip

I am basically satisfied with the performance of the boat........but did think my top end might be higher.

I basicall cruise at ~3600RPM which put me at almost 30MPH......that's pretty good for this boat........I think..

I also have an email into Grady to get some performance numbers.

Didn't take your question as adversarial...........no problems here......

 

[MikDee]

Re: Prop Slip

Sorry Tony i can some times ask a question and it turn's out adversarial....That 24 foot boat is a real chunky bugger. It must handle 3-5' rollers quite well. It would be intresting to listen to a desinger and the reasoning for such short gears in a boat like that. What had me going was a 24' Rinell cuddy that i have been looking at.....With a 350 mag and 1.66 gearing she will do 50+ and its 4000 lbs also..

http://madmariner.com/vessels/power_reviews/story/GRADY-WHITE_OFFSHORE_24_082908_VP

As stated above the boat seems to hit the wall @ 34mph..... I guess if it were mine id be chasing some way to get that hull out of the water but i dont believe they make a prop that can lift that bow up and out....Ill bet she just mashes 3-4 footer's....Does it take heavy schocks well???

I agree, I was doing 40mph with my 4K lb SeaRay, and that was with 79'technology, and a 17' pitch aluminum prop. Yes, I did put center rise manifolds on it with 3" thru-hull exhaust, & Salisbury rubber mufflers, but that was 260 crank hp, not prop hp,,, and the Searay was built like a fish, with a deep vee belly in the middle, leading to a shallow vee at the transom. It would lean to one side or the other easily on plane because of this, and when fully trimmed out, it was skittish because of riding on the flat vee aft, and it's fat belly forced up. My previous 20' SeaRay bowrider had the same hull design, with the 228hp/305 and rode the same way at almost 50, plus was even more skittish at that speed, but less of a leaner.

IMO, that 350 Mag Vortec is not putting out it's full potential.

 

[FreeBeeTony]

Re: Prop Slip

Can it be the prop? I was thinking I was prop'd ok because of my wot #'s....meaning RPM.....not speed.

Seems the prop is slipping alot more towards higher RPM than at cruise.

Will probably try the 17" 3 blade next spring.

Not really looking for more speed, but would like to be set up optimally.....

 

[Tail_Gunner]

Re: Prop Slip

Can it be the prop? I was thinking I was prop'd ok because of my wot #'s....meaning RPM.....not speed.

Seems the prop is slipping alot more towards higher RPM than at cruise.

Will probably try the 17" 3 blade next spring.

Not really looking for more speed, but would like to be set up optimally.....

Ive been searching the net looking at those Grady's...never saw one up on a high plane......Ya know where the boat is riding on the last 1-4 feet of the boat...Most are seem to about 50% in the water i have never seen a good off shore fishing boat skiiping across the blue that i can remeber..Want to try a new prop id go with a Rev 4 in a 14-15 pitch or a stilletto offshore..that boat will need all the grip it can get to lift that hull up..but if youve ever been in big rollers of a 4-5 chop on open water speed isnt to important...but id take that big heavy bow anyday..

 

[bolo78910]

Re: Prop Slip

tony i have 17 pitch mirage plus ss you are welcome to have a test run before you haul the boat, let me know, i am in brooklyn.

 

[FreeBeeTony]

Re: Prop Slip

Thanks bolo............but I'm gonna wait till next spring.
I'm really not too concerned.........and I already have a 17" aluminum 3 blade to try.

 

[FreeBeeTony]

Re: Prop Slip

Just as a follow up............

This year I installed a 17" 3 blade aluminum prop.

I am now running at 30MPH @ 3600RPM and 38MPH @ 4500 RPM (WOT).....I like this alot better than the 4 blade!

My next step (if I decide to) will be a SS 3 blade 15"........if I can find a good used one at a good price.........not sure what kinda improvement I would see.

 

[MikDee]

Re: Prop Slip

That's just about what I figured Tony
I'd say with a good design 15" SS prop, it will be at optimum. That Magnum engine should have enough power to wind up, & get that hull a bit more out of the water with a 15" SS prop

 

[FreeBeeTony]

Re: Prop Slip

What do you think of this prop:

removed link

 

[MikDee]

Re: Prop Slip

It looks Great! It appears to have some nice cupping, & a larger then normal exhaust cone (I think these were noted for this?) for better exhaust flow, I doubt you'll get it cheap, but it seems to be a real good prop.

 

[FreeBeeTony]

Re: Prop Slip

Will keep you posted...........

 

[Tail_Gunner]

Re: Prop Slip

It looks Great! It appears to have some nice cupping, & a larger then normal exhaust cone (I think these were noted for this?) for better exhaust flow, I doubt you'll get it cheap, but it seems to be a real good prop.

As above..Tony edit the link...dont advertise...

 

[MikDee]

Re: Prop Slip

As above..Tony edit the link...dont advertise...

A Wise man! I'm not in the market, nor would I jap somebody I know

 

[FreeBeeTony]

Re: Prop Slip

As above..Tony edit the link...dont advertise...

Done.........and thanks.

 

[QC]

Re: Prop Slip

For clarification (if necessary) a link like that is not a problem with iboats . . . If that link was in the first post of a thread, then it would not be allowed. I guess the best way to understand it is that a link in the first post seems to indicate a desire to sell something or promote a product or site. In this case the link was there for reference and discussion.

If the concern was that someone here might want it and then cost you a higher bid amount, there is no need to worry about that 'cause I just bought it . . . Kidding . . .

 

[FreeBeeTony]

Re: Prop Slip

Thanks QC..........I understand.

Guess I should feel lucky it wasn't a "Buy it Now" auction!!!

 

[Sandhammaren05]

Re: Prop Slip

80% efficiency calculated as if the pitch would be that of a screw through wood is in the right ballpark for a low performance rig. 80% times 16" pitch is (in this case) the pitch of the helical wake that your blades leave in the boat wake. See Dave Gerr's "Propeller Handbook" for a discussion written for laymen.

Negative slip is mentioned below. I've never seen evidence of that and don't believe it. Again, see Gerr's book for better information.



I'm turning a 4 blade aluminum 15X16 prop with a 1.5:1 drive @ 3600RPM going 29MPH (GPS).

The boat is a 24' Grady White ~4000lbs. Bottom is clean.

Does this sound right?[/QUOTE]

 

[FreeBeeTony]

Re: Prop Slip

What?