1993 Carver 280 Express prop selection

[spencerorl]

Hi. I am a long time boat owner of small runabouts and this is my first large heavier boat. The boat has a 7.4 with a Bravo 2.

During my pre-purchase water test i discovered it would only rev to 3500 rpm and about 21mph. The owner said that the boat never ran more than 21mph. He actually had a long block installed about 30 hours ago and confirmed the new engine had a WOT of only 3500 rpm just like the original one.

I found the prop was bent/damaged so hauled it out yesterday and installed a new 18.3 x 19p.
I didnt know what prop size was on the boat until yesterday when i discovered the damaged prop was a 17 3/4 x 21p.

With new 19p prop installed, I ran it again and was able to achieve 4000 rpm. I believe the boat is overpropped and I should put a 17p which, as I understand, should give me ~400 more rpm. This would get the boat in the 4200-4600 operating range.

Does anyone have a 280 (or earlier models 2557 Montego/528 Montego) , with a 7.4 Bravo 2, that could share what diameter and pitch prop they run along with tops speed at WOT?

The boat definitely will rev to 4600 while not under load.
It just seems like the 21p i took off was way to high of a pitch for such a large boat but maybe not.

The prior owner does not know much about boats and had no idea 3500 at WOT was not normal. I knew something was wrong immediately when we got on plane.

Last, I'll add the timing was checked yesterday and it's set at 8° BTDC and verified the secondary butterflies are opening at WOT.

Thanks in advance for your thoughts!
Mark

1987 Checkmate Enforcer 7.4 Bravo 1
1985 Checkmate Enticer with 115 tower of power
2015 Premier Tritoon with 200hp

[waybomb]

Welcome aboard!
Someone here must have one like your that can help you.

[bud37]

Source of the post The boat definitely will rev to 4600 while not under load

Welcome to the forum.....can't help with your boat model , I am sure someone may chime in with some prop help for you. I do think you may be on the right track though.

I will comment on the engine revving that high unloaded....that is not an indicator of anything as an engine can rev with very little fuel, timing, even dead cylinders etc....also not a good idea mechanically ( valve train )

[km1125]

IIRC, Bravo II's came in a bunch of drive ratios (1.5-1.8-2.0-2.2?). You'd need to know what you have and what whatever boat you're comparing to had in order to make an apples-to-apples comparison on prop sizes. If the boat was repowered at any point they also may have changed drives or ratios to adapt to the new engine, if different from stock.

[spencerorl]

Thank you. I guess I will search for that this spring when the water is warmer.