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Darwaypen

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I have a 2005 23' 5000lb Monterrey, I have recently replaced the original 305 MPI Alpha 1 Gen 2 with a 383 MPI and a Bravo 1 with a 1.5 gear ratio.
The 305 prop was a 4 blade Solas 14/1/8 x 19. The Bravo drive i installed already had a Mirage 3 Blade 14 3/4 x 21 on it, it was hooked up to a 496 in its previous life. I also have a Power tech 14 1/2 X 16 that i have never run and an Aluminum Hustler 14.5 x 17.
I took the boat out for sea trial with the 3 blade on it, it comes outta the hole pretty good, but would only pull up to 4000 rpm and GPS speed was 48mph. Are any of the props the right size for my application? I am looking for a good all around prop, strong out of the hole with decent top end.
Just looking for opinions from you guys that have been doing this for awhile.
By the way, these forums were the ONLY way i made it through that complete motor and outdrive swap, thank all you guys for that!
 
OK,
You listed 4 props in your post.


START OVER and be specific! what prop did you use when you were out on the water?


On a three blade prop, you will gain ~ 300 rpm for a drop in pitch. (21 pitch = 4000 rpm go down one pitch to a 19 pitch and you would achieve ~ 4300 rpm)

The 383 I would think is rated around 5000 - 5200 rpm for wide open throttle operation.


So you may have a gear ratio miss match with your drive if you are only hitting 4000 rpm with a 21 pitch.

Its a long way to get to 5000 rpm. (if 21 pitch =4000 you may need a 15 pitch to get close to 5000 rpm with a 3 bladed prop and theoretically a 13 pitch would put you right in the sweet spot of 5000-5200 rpm) This is typically indicative of a ratio issue.

I am no expert on ratio to prop pitch but that is my understanding


What I would do if I were you,

Which ever prop you used to get to 4000 (which you did not specify), switch to each one and record results.
List results and then a proper decision can be made to suggest what to do next.

Simply throwing out a bunch of prop sizes and hoping for an answer is not a good way to figure this out. DO SOME WORK and get data.

Because you changed the OEM design this would be the correct process to determine which prop size/pitch works best
 
You need the help of a prop shop. They will help fit and test the correct prop. It takes several tries to get it right and that's what they do. Since you have 4 props already, maybe you can work a deal with them. Maybe you already have the right one and don't know it.
It's part science, part black art.
You can't just make blanket statements about what prop to use without real-world testing as every boat is different. It really is money well spent. You get better performance and fuel efficiency which eventually will pay for the cost of the consultation.
 
The correct prop is that prop which allows you, with a 3/4 to full tank of gas, normal load ( passengers and gear) and good tune, calm seas , to achieve a maximum wide open throttle RPM that is within the WOT rpm range specified for your engine. I've done several reengines and have discovered that the oft quoted 2000 RPM change per pitch change, is a crude starting point. Gasoline engines do not have linear rpm vs torque curves. Soooo... it is often trial by error :) Enlisting the aid of a reputable prop shop is a good way to go.
 
Thanks for the replies, the initial run was with the 3 blade that came with the Bravo drive. I am going to go out and have a "prop day" and see which others perform the best. I was just wanting to know from you guys experience if any of these would be even close.
 
I did mention the sea trial was with the 3 blade prop....
I had to go back and read it to be sure myself.​



I have a 2005 23' 5000lb Monterrey, I have recently replaced the original 305 MPI Alpha 1 Gen 2 with a 383 MPI and a Bravo 1 with a 1.5 gear ratio.
​
The 305 prop was a 4 blade Solas 14/1/8 x 19. The Bravo drive i installed already had a Mirage 3 Blade 14 3/4 x 21 on it, it was hooked up to a 496 in its previous life. I also have a Power tech 14 1/2 X 16 that i have never run and an Aluminum Hustler 14.5 x 17.
I took the boat out for sea trial with the 3 blade on it, it comes outta the hole pretty good, but would only pull up to 4000 rpm and GPS speed was 48mph. Are any of the props the right size for my application? I am looking for a good all around prop, strong out of the hole with decent top end.
Just looking for opinions from you guys that have been doing this for awhile.
By the way, these forums were the ONLY way i made it through that complete motor and outdrive swap, thank all you guys for that!

 
Darwaypen said:
I did mention the sea trial was with the 3 blade prop....
I had to go back and read it to be sure myself.​



I have a 2005 23' 5000lb Monterrey, I have recently replaced the original 305 MPI Alpha 1 Gen 2 with a 383 MPI and a Bravo 1 with a 1.5 gear ratio.
The 305 prop was a 4 blade Solas 14/1/8 x 19. The Bravo drive i installed already had a Mirage 3 Blade 14 3/4 x 21 on it, it was hooked up to a 496 in its previous life. I also have a Power tech 14 1/2 X 16 that i have never run and an Aluminum Hustler 14.5 x 17.
I took the boat out for sea trial with the 3 blade on it, it comes outta the hole pretty good, but would only pull up to 4000 rpm and GPS speed was 48mph. Are any of the props the right size for my application? I am looking for a good all around prop, strong out of the hole with decent top end.
Just looking for opinions from you guys that have been doing this for awhile.
By the way, these forums were the ONLY way i made it through that complete motor and outdrive swap, thank all you guys for that!

Click to expand...

Yes you did but it does not specify WHICH 3 BLADED PROP???????????????????

"" The Bravo drive i installed already had a Mirage 3 Blade 14 3/4 x 21 on it, it was hooked up to a 496 in its previous life. I also have a Power tech 14 1/2 X 16 that i have never run and an Aluminum Hustler 14.5 x 17.""

Just sayin.....................
 
The majority of small and medium sized pleasure boats are designed to run 19-21 pitch 3 balded props from the factories.


You could reach out to the Monterrey Company and ask them what they suggest with your re-power configuration. This is done a lot, so they may be willing to advise on starting point based on your preliminary results as they are the design experts of their own products.
 
My bad Kgohst, the mirage is the only 3 blade in the bunch, all the others are 4 blade. I did reach out to Monterey Boats, they would not give me recommendation for my power swap, but gave me what the boat came with from the factory, which was a Merc BM-Al- 14.5x19 3 blade prop. Gonna take her out tomorrow with my Aluminum 4 blade 14.5x17 and see what she does.
 
So i ended up putting my Stainless 4 blade Solas on, 14 1/8 x 19, she came outta the hole plenty hard, nose never even came up, ran her up to 4900 rpm, verified with my Snap on timing light, GPS said 51MPH. i think i'm happy with the overall performance of that prop. That 383 compared to the 305 is unbelievable! Thanks for the replies guys!
 
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