Bravo 3x props - Where to start?

[PCUK]

I've asked this before but no-one seems to know anything about choosing the correct props' for a specific boat and engine.
LWL 24ft
Beam 7ft at WL
Disp 3000Kg
250hp @ 4200 rpm
2.2:1 gear ratio
Anyone want to suggest a prop' set to start with.
Thanks.

 

[Mr Googler]

| Mercury Marine

 

[QBhoy]

Hi. Tell me more. I’ll have a go. I know of a few boats featuring similar (but not identical specs). I happen to be aware of some of their data with certain pitches on their bravo3.
But first can I ask more around your situation?

Is this an original set up and matched engine to outdrive from new ?

I presume there are no props on there just currently as a base line to go by ? Or perhaps there is but you’re not able to test or gather data ?

Regarding the engine. I’m presuming your mention of 250hp, is referring to the 5.7 mercruiser 2 barrel carb engine ? If not, please correct me ?
Perhaps thought I’d also ask around the rpm figure you have there too. Not with the intention of doubting you at all, but most of these engines (if I’m correct in thinking she’s the 5.7 and from the last couple of decades or close) at or around the 250/260hp type…would have an rpm range of 4400-4800, ideally being propped towards the top of that range too. Exception to the above would be the mpi version, with their higher rpm range. Other end of that would be much much older engines, some of which had a slightly lower rpm range the other way.

Is she definitely a 2.2-1, rather than the other (and perhaps more common) 2.0-1 ?

Anyway. Any details you can manage around the above or additionally, I’d be happy to give examples from what I know in other boats.

 

[PCUK]

Thanks QBhoy, you're wrong on just about all of your assumptions but that's cos' I didn't provide enough info'.
Boat is a 1978 Reinell V-204.
Stripped for almost bare shell rebuild. And before all the naysayers jump in, I'm not interested in the cost and eventual loss, I'm doing it cos' I want to!
Engine is a new Vetus 250VF 5 cylinder diesel. Drive is 2.2:1.
Can't think of anything else pertinent at the moment.

 

[jointventureII]

Following this with interest, I'm looking to upgrade my Bravo 2 to a Bravo 3X, similar boat & engine specs

 

[QBhoy]

Thanks QBhoy, you're wrong on just about all of your assumptions but that's cos' I didn't provide enough info'.
Boat is a 1978 Reinell V-204.
Stripped for almost bare shell rebuild. And before all the naysayers jump in, I'm not interested in the cost and eventual loss, I'm doing it cos' I want to!
Engine is a new Vetus 250VF 5 cylinder diesel. Drive is 2.2:1.
Can't think of anything else pertinent at the moment.

Whoa. Got you. Never saw that coming at all !! Brilliant stuff !
That explains the rpm of course. The diesel makes things a little more complex.
All I can do is come back to you with some numbers from Petrol boat examples. Do a few experiments on assumed prop slip etc etc. she sounds lovely !

 

[QBhoy]

PC. Any pics of the boat and also any details of how they performed with their original power plant ? All I can see for a v204 is a more modern 90’s/00’s 20ft bowrider thing. I presume with this one of yours being 3000kgs and 24ft…it’s a much bigger thing. Is she wooden or grp ? Be good to know ball park figures of how they perform with similar Petrol power or what ever they once had in them.
If she’s expected to be around a mid 30’s or perhaps a few mph more..we are likely talking about a set of 24” props as a ball park. Couple of realistic figures using an assumed speed in the mid 30’s and if able to achieve the 4200 rpm. 15% slip is a decent figure to be aiming for, perhaps she’ll be a little higher from a first effort, given the unknowns at the minute. These props aren’t cheap at all and could end up an expensive guessing game. But if you get a set of 24’s for a good price. That is a fairly common pitch and always sought after used. Won’t be an issue selling them on again, if at the right price to start with. These props are all stainless, as you’ll know. The additional complexity when propping a diesel, a turbo diesel in particular, is the need to not only get the right pitch for top end rpm suitability…but ensuring that there is suitable pitch there to load up and spool the turbo, down low in the rpm too…as you’ll know. Anyway. Around the 24” mark might be a good starter for 10..won’t be too far out, either way I’d think. Unless she has a pace expected that’s way off my assumptions. See what you think

 

[PCUK]

Thanks Q, here's a pic' of the boat when we had just collected it. Everything has been removed and scrapped including windows, rails and rubbing band. Hull is a shallow vee.
I haven't got any decent exterior pics of her current state but here are a before and after on the helm and instrument panel.
No performance figures as I never saw it leave the marina and when I got it, it was laying on the ground in the yard.
Regarding the prop' figures I thought the sizes were presented as numbered sets with various combinations of three and four blade props'.
Also, do you happen to know of any prop' suppliers that offer decent discounts?
Thanks for all your hard work so far!

 

[QBhoy]

Thanks Q, here's a pic' of the boat when we had just collected it. Everything has been removed and scrapped including windows, rails and rubbing band. Hull is a shallow vee.
I haven't got any decent exterior pics of her current state but here are a before and after on the helm and instrument panel.
No performance figures as I never saw it leave the marina and when I got it, it was laying on the ground in the yard.
Regarding the prop' figures I thought the sizes were presented as numbered sets with various combinations of three and four blade props'.
Also, do you happen to know of any prop' suppliers that offer decent discounts?
Thanks for all your hard work so far!

She looks beautiful. Stunning.
So these bravo 3 props..they most commonly or maybe even exclusively, come with a pair of 3 blade stainless props. Any I’ve seen, pitched with an even number. As in 22”, 24” and 26” for example.
That said…there was a specifically made bravo 3 outdrive produced, specifically with diesels in mind. I think they may even have said diesel on the decal or bravo x or something like that. Perhaps they came with 4 or 4/3 blade combos, like the Volvo Penta DP’s did for diesel. Not that I’ve seen in person though. You’re lucky she’s a bravo 3 and not a VP DP. Should you have to start from scratch pitching a VP DP…jeez, it’s a minefield of confusion and hidden pitch figures !
One particular boat i was very familiar with, was a 24/25ft large cuddy type sports boat. She weighed probably around or just over 2t. She had a 350 mag mpi Petrol with 300hp. Rpm range was 4600-5000. Gear ratio I’m sure was a 2.0-1. She had 26” props on her B3. Stepped and fairly quick hull design.
She ran a many times proven 50 mph gps at 5000 rpm or a tiny bit over.

I have a friend with a 26ft heavy baja boat. She has b3 drive and currently messing with pitch. Just because the engine she now has, is a built 6.2 stroker, with much more power and rpm to play with, over the original engine. I’ll get more details from the owner soon.

I also know of a guy with a 25ft American cabin cruiser (of the generic type). That has a 5.0 mpi 260hp in her. Bravo 3 drive. I’ll find out what props he has and how she runs..she might be closer to your weight and power I’d think.

As said earlier..should you see a set of 22’s or 24’s for a few hundred quid..I’d grab them for sure. You’ll always be able to sell them on at that common pitch..not losing or even gaining money. The cost new, is just eye watering.
As for aftermarket…I’m not sure in terms of the b3 particular props..I know that Michigan Marine likely do the best quality aftermarket props for the VP DP drive…but these came commonly with ally props (as well as stainless too) meaning aftermarket was easily available. Should they in fact offer stainless props (b3 all are) for each either brand..I just don’t know.

 

[PCUK]

Thanks Q, I understand that the 3x was designed for diesel having stronger internals. I think we are getting somewhere now as I am getting a better understanding of what is involved.

 

[QBhoy]

Thanks Q, I understand that the 3x was designed for diesel having stronger internals. I think we are getting somewhere now as I am getting a better understanding of what is involved.

Excellent. Hope I might have helped a little at least. You’ll know as well as I…the more ball park figures you can gather together around similar or even same (with their original power plants) examples, in terms of performance etc…the more equipped you are to make assumptions or best guesses for a set of props. Keen to hear how you go, going forward with her. Lovely looking thing.

 

[ChromeDome]

To make calculations or realistic estimates, the normal good-to-go GW is needed. All in.

Difficult at the moment, but weight is crucial for planing boats' performance.

 

[QBhoy]

To make calculations or realistic estimates, the normal good-to-go GW is needed. All in.

Difficult at the moment, but weight is crucial for planing boats' performance.

What is GW ? Likely I’m being daft..but it’s not immediately coming to mind . Ta.

 

[GrahamHR]

Try out the American Four Winns site; customer support, it might be the "fact facts". They indicate all the props fitted to their boats model by model ( SX, DPS, DPH, Bravo 1, Bravo 2, Bravo 3, X etc.) It'll give you an idea of where to start

 

[PCUK]

Well CD I guessed the gross weight at about 3000kg based on how she sits on the trailer.
I'll certainly give the Four Winns site a look Graham.
Thanks all.

 

[ChromeDome]

What is GW ? Likely I’m being daft..but it’s not immediately coming to mind . Ta.

Sorry,- meant the GrossWeight of boat, engine, driveline, gear, crew and what else the 250 horses have to push.

The subject was touched on in 2014 when PCUK first mentioned the boat
Power to weight ratios for performance and economy

If, say, the GW ends up being 2750 kg and the hull is a modified V, 250 horses will be able to push it to a max speed of approx. 32 knots, propped correctly.

4200 rpm reduced 2.2:1 makes 1909 prop shaft rpm. For 1909 rpm to do 32 knots it needs a pitch of 20.15", not factoring slip in.
Calculated, of course

 

[QBhoy]

Sorry,- meant the GrossWeight of boat, engine, driveline, gear, crew and what else the 250 horses have to push.

The subject was touched on in 2014 when PCUK first mentioned the boat
Power to weight ratios for performance and economy

If, say, the GW ends up being 2750 kg and the hull is a modified V, 250 horses will be able to push it to a max speed of approx. 32 knots, propped correctly.

4200 rpm reduced 2.2:1 makes 1909 prop shaft rpm. For 1909 rpm to do 32 knots it needs a pitch of 20.15", not factoring slip in.
Calculated, of course

Admiring the detailed mathematics there ! Excellent stuff. Think you won’t be too far off with assumed speed there. Thought similar myself too. Ah…what I’d do to achieve a magical 0% slip !! Alas, an impossible goal I’m afraid..as you, I and many others will certainly know.
A slip of 15 or close, I thought of realistic value. Hence my starter for 10 opinions above.
On a side note of slip..I’ll admit a very unhealthy obsession with and around the futile quest for propeller perfection. An expensive affliction for sure. Although I have managed down to a slip of about 3% on my cherished boat..and from memory, about 6/7% on my fletcher cuddy with outboard. Not bad I think. Although some could argue that the experimenting and end result, may not outweigh the expense and hassle