Purchasing a new prop

[Kdaddy]

I own a 1991 Larson Legacy 20' bowrider. I want to go with a stainless prop but have no idea what diameter or pitch to start with. The old prop is badly damaged and I cannot read the size. The boat has a 5.7l with alpha 1 drive. Can someone help me?

 

[QBhoy]

We can help, but need to know the must have details first.
Current prop fitted
current max rpm and gps speed wot and trimmed well
currenr gear ratio

if nothing else...certainly need to know current performance characteristics and current prop.

All the best.

 

[alldodge]

Agree with QBhoy we need more info. Not knowing what the prop pitch is, and also not knowing if the drive was ever replaced I'll say, it probably had a 19 or 21 pitch on it.

Suggest going to a prop repair shop and ask them if they have a loner program, most do. Install one and then give it a try and record numbers

WOT RPM
WOT speed with GPS
Determine the drive ratio

 

[QBhoy]

Yeah. Likely a 19”....but so important to get a properly dialled in prop. Be great to know the details requested.

 

[Texasmark]

Find yourself a reputable prop shop. Give them your details. Get a couple of their suggestions and take them out for trial. Best way to get your best matched prop.

On running a "loaner to buy" prop, put it on, take the data in known clear water, and take it off....shine it up and put it back in the box. Wink. If you don't buy it somebody else may want to and after all it IS a new prop and needs to look like one for the next customer. Expect to pay for any damage.

If not happy, tell them what happened and retest with their next suggestion. It will cost you more money initially, but this way you have a super chance of getting the right prop rather than wild blue shotgunning which, I guarantee you, will cost you more in the long run and you may quit feeding the "sink hole for money" before you find what suits you. Good luck

 

[QBhoy]

Any news on this ? Apologies if the above sounds a little condescending...just that when new guys post a post like yours...the folk trying to help or advise need to try and cover all bases with regards to your current knowledge, experience and set up.
There are many guys out there (perhaps like yourself) that have plenty of boating experience, but prop selection has never crossed their mind, or even had to. It was nearly 25 years of boating for me without it even being a second thought.
Now knowing what a difference it can make, let alone affecting the health and longevity of the engine, it’s an obsession of mine...for better or for worse.
One thing is for sure though. I can’t tell you how great it is to get a properly dialled in prop. Best thing you’ll ever do for your boat, in terms of useability, performance and efficiency. Worth every penny and consideration.
Just as an example...my wee boat gained around 9mph from standard ally, to one of the props I have. And 7mph with the one I use mostly. Added to this the much better fuel economy and all round suitability for cruising, water sports and the likes.
Would love to help you out, if you can find the time to post a few details. That’s what we are here for.
All the best, Allan.

 

[76SeaRay]

Not trying to steal a thread but asking the question differently may also help Kdaddy. I am in a similar situation however mine is a restoration of a boat and I have no information on any performance. It will be a 5.7L (hopefully Vortec) with an Alpha One Gen One 1.50 to 1 gear ratio. Boat will be run at low altitude (almost sea level) most of the time. Boat empty weight is about 3800lbs. It is a 1976 22 foot SeaRay cuddy cabin with hardtop. I need to buy a prop to get any performance information to get to the right prop. So, asking the question differently, anybody have a suggestion on what is the best prop to buy "as a starting point" to get a baseline performance from which to tune? Pitch, diameter, and number of blades??

Thanks....

 

[Sea Rider]

If engine counts with a prop there's your starting point assuming is in good condition. Test at wot as usually loaded on flat calm water cond, check if inside min- max wot rpm range factory stated. If with no prop use a prop selector and go from there maximizing a prop that best suits your particular boating needs.

Happy Boating

 

[76SeaRay]

Thanks for the info. Again, I have no prop on this restoration so no current data. Prop selectors don't fit well with older boats and lead to more confusion than answers. So, that said, I am just going to guess based on what reading I have found and just look for a three blade 14.25 x 19 or a 14.5 x 19 and go from there. Kdaddy, your boat seems a bit lighter in weight and 2 foot shorter than mine. I don't know how much diameter or pitch changes for changes in boat size and weight so not sure if this helps you but it might give you some ideas on where to start.

 

[Scott06]

As a general rule of thumb drive assuming it is original will be geared that props pitched from 17"-21" will cover the gamut. Typically 17" will give good pull for watersports or heavy load, 19" general all around use, 21" light loads and top end.
If your not sure as a starting point as mentioned find a prop shop try before you buy. Start with a 19 which likely will work ok.

 

[QBhoy]

Not trying to steal a thread but asking the question differently may also help Kdaddy. I am in a similar situation however mine is a restoration of a boat and I have no information on any performance. It will be a 5.7L (hopefully Vortec) with an Alpha One Gen One 1.50 to 1 gear ratio. Boat will be run at low altitude (almost sea level) most of the time. Boat empty weight is about 3800lbs. It is a 1976 22 foot SeaRay cuddy cabin with hardtop. I need to buy a prop to get any performance information to get to the right prop. So, asking the question differently, anybody have a suggestion on what is the best prop to buy "as a starting point" to get a baseline performance from which to tune? Pitch, diameter, and number of blades??

Thanks....

Starting point would be a 19” black max ally prop

 

[Texasmark]

Not trying to steal a thread but asking the question differently may also help Kdaddy. I am in a similar situation however mine is a restoration of a boat and I have no information on any performance. It will be a 5.7L (hopefully Vortec) with an Alpha One Gen One 1.50 to 1 gear ratio. Boat will be run at low altitude (almost sea level) most of the time. Boat empty weight is about 3800lbs. It is a 1976 22 foot SeaRay cuddy cabin with hardtop. I need to buy a prop to get any performance information to get to the right prop. So, asking the question differently, anybody have a suggestion on what is the best prop to buy "as a starting point" to get a baseline performance from which to tune? Pitch, diameter, and number of blades??

Thanks....

As I stated numerous times before. If starting from scratch consult a prop shop with proven performance. The ones I have used will loan you a prop to do the ultimate.......run it on your rig. If you don't like it, bring it back and tell them what you didn't like about it......take out prop #2 and run it. If you don't like it........................

Just remember you are borrowing to purchase and if you don't someone else will be in the shop to borrow to purchase a "new" prop. Therefore prop needs to be returned in the same shape as your receiving it.

Yes you will pay more for that prop/service but ask yourself this: Why are you boating? How much do you have invested in it? Does it matter to you to have a great outing experience vs just a ho hum time that you could have sitting in front of the TV on a Sunday afternoon with beer and pop corn?

The prop, if SS can easily last the life time of the engine. I bought one of the first OMC Stainless Steel Teflon props back in '73 to put on my new '72 boat when OMC finally came out with SS. The prop lasted me the 7 years I had the boat and the last time I heard from the new owner he was still running that prop for which I paid$185......lots of bucks back then. However average that over the life of the rig and it doesn't even register.

Good luck in your quest.