Want your experience with Alpha 1 prop selections

[blubayou]

The problem is my current set up spins the prop up pretty bad, blows out in turns while spirited driving, Current set up, 3 blade 14 x 19SS perfect condition, 20ft open bow with 355ci top speed is 57mph (GPS) and running 6k, or at least my gauge pegs at 6k. At this moment I am on a < $175 budget for a replacement prop. Looking at Solas Amita 4 blade 14 x 21 or QL 4 blade 14 x 23.
Looking forward to your comments, thanks!

 

[steelespike]

Re: Want your experience with Alpha 1 prop selections

Is this motor intended to operate at this sky high rpm.Wouldn't seem like it would hold up too long at that rpm.

 

[blubayou]

Re: Want your experience with Alpha 1 prop selections

No, the engine is not built to run 6k for extended periods. The cam is speced to 5500rpm and it has a cast crank and so forth and so on. It's a budget high performance build. Plus I don't plan to run it up and down the river topped out. It's a recreational boat and will spend most of it's time pulling folks from tubes to slalom skiing and a flex of it's muscle from time to time.
Now, let's get back to business, do you have experiance in such applications?

 

[Bondo]

Re: Want your experience with Alpha 1 prop selections

No, the engine is not built to run 6k for extended periods. The cam is speced to 5500rpm and it has a cast crank and so forth and so on. It's a budget high performance build. Plus I don't plan to run it up and down the river topped out. It's a recreational boat and will spend most of it's time pulling folks from tubes to slalom skiing and a flex of it's muscle from time to time.
Now, let's get back to business, do you have experiance in such applications?

Ayuh,.... It might be able to spin 23"s.....

A 21" will no doubt drop the rpms down abit,... donno How much...

 

[blubayou]

Re: Want your experience with Alpha 1 prop selections

I ended up ordering a 4 blade 14x21AL. Going from a 19 to 23 is a large step and I was concerned that I would lose responsiveness during water sports. I will report out on the performance so others can use this experiences as a reference.
I'll be back in a week or two.

 

[steelespike]

Re: Want your experience with Alpha 1 prop selections

Sorry I didn't get back I was a little mystified never heard of a 355 or what it might be made from.I also should have asked about any details you could help us with. Is it an I/O do you know the gear ratio?
I should have had you read "read this first" at the top of the prop forum.
Guessing your slip at 10% and using 6000 rpm I get a gear ratio of about 1.7.
Using the same ratio and slip and guessing rpm the 4 blade 21 could produce about 57.
Thats a lot of guessing and who knows if the 6000 was accurate.

 

[blubayou]

Re: Want your experience with Alpha 1 prop selections

steelespike
I read the "read this first" after I made the post but I was close on the specs. My title reads Alpha indicating a I/O but I didn't include that is has a 1.65 gear ratio. The 355ci is a smc 350ci bored 0.030 over giving you 355ci. The 14 x 19SS was dilivering 57mph on GPS.
Thanks for the calculation.

 

[blubayou]

Re: Want your experience with Alpha 1 prop selections

Installed a solas 14 x 21 4 blade and here is the update. Before I start, I ordered the prop from iboats and it showed up three days later. Thumbs up on shipping!

Although the last carb adjustment isn't right the prop made a significant difference. For starters it's doesn't spin up under hard acceleration anymore! Doesn't blow out in turns and WOT rpm dropped from 6k to 5k. The new prop is more responsive to trim adjustments. Although I would have like to have had a accelerometer to measure vibes, it subjectively has less vibration. It may be slightly more maneuverable at slow speeds but the rough idle from a bad carb jet selection made it difficult to accurately evaluate slow speed maneuverability, could be in my head.

Summary: It had been recommended from the local prop shop that a 23 pitch would possibly be the proper prop selection. After installing the solas 14 x 21AL prop I am very pleased that I decided to go with the 21 vs 23. Considering we wakeboard, slalom and tube more than just cruise, today?s sea trial strongly support the 21 pitch was the better selection for my purpose.

 

[spdracr39]

Re: Want your experience with Alpha 1 prop selections

Glad you found what you needed. If the 2"pitch changed the rpm that much there was probably something wrong with your other prop.
+1 on Iboats service and shipping