prop ?????

[slavka]

Hi I have a question about the prop i have 1991 180br sea ray with 4.3L and alpha1 out drive and my prop is 14x19 and full throttle at 4800 rmp at about 40mph. And i wanted to know if i can go to 21pt prop and will i still be able to tow tube with two or more peaple?

 

[175BR4.3]

I am still learning about props, but i have asked similar questions recently, and have been doing some research..... With that in mind, here is what i have learned..First off do you currently have an aluminum, or stainless prop?...The reason i ask, is i currently have a stainless, that i had rebuilt a week ago, while it was in the shop i borrowed an aluminum prop so i could still get out on the water.

With a 14x19 Aluminum prop i was able to run 41-43 MPH, and was able to slightly over rev the motor to ~4950 RPM's

With a 14.25x19 Stainless Prop i rum 47-49 MPH at 4800 RPMs.

So just by switching that little bit, makes a huge difference.

Whay are you wanting to go to a 21p??

 

[springer3]

The answer is yes, you have plenty of power, but I don't think you will like a prop that is too large. It will take a long time to get on plane, and you will lower your top speed, possibly by a lot because the engine will not be able to produce full power. You might hurt your fuel consumption as well.

 

[slavka]

I am still learning about props, but i have asked similar questions recently, and have been doing some research..... With that in mind, here is what i have learned..First off do you currently have an aluminum, or stainless prop?...The reason i ask, is i currently have a stainless, that i had rebuilt a week ago, while it was in the shop i borrowed an aluminum prop so i could still get out on the water.

With a 14x19 Aluminum prop i was able to run 41-43 MPH, and was able to slightly over rev the motor to ~4950 RPM's

With a 14.25x19 Stainless Prop i rum 47-49 MPH at 4800 RPMs.

So just by switching that little bit, makes a huge difference.

Whay are you wanting to go to a 21p??

Well I have a aluminum prop. its 14.19 and i just wanted to have a little more top speed and not to lose much of power. I guess i can do 14x20 still one. Thank you

 

[springer3]

If your WOT is 4800 RPM, a larger prop will make you slower. The engine has a power curve for WOT. It peaks around 4800 RPM, and that is why you get the best speed when your prop keeps the engine at peak HP. Bigger loads lower the WOT speed, and you make less power. Less power = less speed.

 

[Lazy Daze]

Sometimes a stainless prop of the same pitch will give higher top end. It really all depends on the hull/engine match-up. It should definitely give better hole shot.

I'm not sure of "off brands", but Merc 3-blade props come in odd-number pitches, while the 4-blades come in even number. Meaning you'll have to go to a 23" if you go up in pitch. That'll be too much for sure.

 

[Knotty Buoy]

I've just sold my 180 with the same engine,
I had three props for it.
19" , 21" , and 23" stainless.

19".....42 mph
21".....46 mph
23".....49 mph......(one up)

The 23" would still come up on the plane with four adults and 1 kid on-board and do 47/48mph but untill I fitted fins on the cavitation plate it struggled a bit to gett on the plane with that load. (had to move people about the boat). No problem with fins. I've towed inflatables with adults on board with this prop but the engine revs are quite low and it tends to keep falling of the plane if you try to keep the speed down to 20 mph with this prop.

The 21" was a nice compromise. would pull up a (Big) skier and still give good economy (Petrol £5 a gallon!!). Not a 100% certain it would pull a mono.

The 19" Pulled up three skiers but topped out at just over 40mph.

If I'd had it I think the ideal prop for this boat would be a 21" stainless.

The fuel economy improved with each incriment of the pitch but I wouldn't go any coarser that the 23"

Best of luck.:grin:

 

[slavka]

I've just sold my 180 with the same engine,
I had three props for it.
19" , 21" , and 23" stainless.

19".....42 mph
21".....46 mph
23".....49 mph......(one up)

The 23" would still come up on the plane with four adults and 1 kid on-board and do 47/48mph but untill I fitted fins on the cavitation plate it struggled a bit to gett on the plane with that load. (had to move people about the boat). No problem with fins. I've towed inflatables with adults on board with this prop but the engine revs are quite low and it tends to keep falling of the plane if you try to keep the speed down to 20 mph with this prop.

The 21" was a nice compromise. would pull up a (Big) skier and still give good economy (Petrol £5 a gallon!!). Not a 100% certain it would pull a mono.

The 19" Pulled up three skiers but topped out at just over 40mph.

If I'd had it I think the ideal prop for this boat would be a 21" stainless.

The fuel economy improved with each incriment of the pitch but I wouldn't go any coarser that the 23"

Best of luck.:grin:

Thank you that is wary use full information but one more question 21p is it 14x21?

 

[Knotty Buoy]

Hi

The 19" has a Fourteen and a half inch diameter.
The 21" Has a Fourteen inch diameter
The stainless I'm afraid went with the boat but it was a standard 3 blade Laser II prop.
Unless I was skiing with the boat I used the 23 stainless.

As well as the economy the boat was significantly quieter with that but it did need Doel Fins on the drive to make it practical.

Cheers :grin:

 

[gruz1]

Knotty bouy, how did you get the 4.3 to run a 23 prop. I have a little bigger boat a 190 with the 5.0 and it won't turn a 23. Did the fins bring up the rpms.

21 aluminum rpm 4900 top 47
23 SS rpm 4300 top 46

I'm trying to find a used 22. Wonder if a 4 barrel would help.

 

[Knotty Buoy]

Your 190 is quite a bit heavier than the 1989 180CB that I had (about 400lbs) but I'm surprised that your dropping 600 RPM with two inches. Would normally expect 300-500. Also 4900 is right at the top end for the engine. I have no doubt that the change to a four barrel would buy the extra RPM with the 23" if it's a two barrel that's on it just now but here a "four barrel" would probably cost more than a second-hand engine. The fins won't bring up the WOT revs at all they just reduce the "nose-up" attitude as the boat comes out of the hole...................I'm probably misjudging you, but I suspect this is all to see that needle on the other side of the 50 mark? :grin::grin:

 

[Nehalennia]

Yes, buy a 21" High Five stainless prop. The boat you have was my first boat. It was a great set up and the High Five Stainless prop gave you the hole shot but perfect bow rising cruise for that size of a boat.

 

[gruz1]

I'm probably misjudging you, but I suspect this is all to see that needle on the other side of the 50 mark? :grin::grin:[/quote]


No, Your right. I would also like to cruise at a little faster speed. Right now with the 21 at 4000, I'm cruising at 37 or 38. The 23 is more where I would like to be about 43. But I don't want to run this prop if it is going to ruin the motor. What I really need to do is get a 21 stainless.