Prop Selection and RPM

[777]

So I just switched my Seasport 2200 to a duoprop (AQ-290, now DP) with the 305CI AQ-211-A. Wow, what a difference. I expected a better hole shot, but wasnt' expecting how quiet, smooth, and most of all how much different the handling is. The whole boat seems to plane higher, it's almost like it's riding on a cushion.

Not knowing which props i'd need I started with a used set of C4's (I think). The boat now tops out at like 4200-4300 RPM with 2 guys and a half tank of fuel, where as with my single prop, it could go over 5000 (I'd only do it briefly).

Question: is this too much prop? Is it enough to be concerned about? When the boat is loaded, the RPM will limit out even lower, right?

thanks!

 

[wolf]

what size motor basically a 350 chev is supposed to be between 4000 to 4500 i believe mine runs WOT with the 290 duo at 4300 to 4400 loaded so im happy with that dont want to go too low.
id try the next size see what it does
good luck Wolf

 

[Fixit]

never rana duo prop myself, but i try to prop the boat so that its100rpm above max rpm when uberlight, ie no gear, empty tank, one person.

99% of the time its never possible to achieve that over rev, but gives good performance the other time

my 2008 mercruiser 350 mag mpi has a max rpm range of 4800-5200

 

[Sr SQ]

I would get the rpm back up to the 5k range so your not lugging the engine so hard.
Yes more load=less rpm
Ideally you shoot for max rpm with average load, that allows for occasional runs heavily loaded…… some boats are always loaded to the gunwales so that will be their average load.
Over propping a marine engine is the quickest way to kill it.

 

[wolf]

i personally thank 5200 is too high im thinking its way lower than that in the range I said but id phone a prop or merc/volvo dealer to get the proper rating.

word of advice

 

[wolf]

so here is the chart thing ive alwatys used as it covers all kinds of engines as you can see the "zone" where you want your RPMs to be at i was close its 4200 to 4600 RPM at WOT , i tested my engine today full of gas and water and 2 guys at it was at just a titch over 4400 rpm and thats with C4 ss props. the experimenting stage is always the challenge

Good luck my friend

inboards rock

Wolf