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I just purchased a 2005 256ssi with a Volvo 5.7 liter and a duo prop drive. It has twin stainless steel props on it. and a through hall exhaust.  I have a couple of questions as to what my reasonable expectations of speed should be versus what the previous owner said they were for him. 

A. The previous owner told me that he gets "every bit of 50 mph." Although I was skeptical, when I maxed at 44mph @5000 RPM (gps speed) I was a little shocked given the engine and drive combination. The conditions when I got 44 were smooth water, 3 people (400 pounds) and (lets say) a full tak of fuel (70 gallons). 

B. The props have some dings and dents. (my background is in single aluminum props in a small shallow lake). I know the effects of a dented or bent aluminum prop, however will dents and nicks in a SS duo prop  slow the boat that much?

C. What is the max RPM at full throttle for this boat. I was at 5000 RPM with the trip 1/2 up after I got onto plane and still 44mph.

D. I have been looking online for information on the duo props with little luck. Are the diameter /pitch calculated the same way as the single aluminum props (14 /19 etc). Should I change the pitch of the prop to get additional top end. 

Before judging, I completely understand that I am chasing 1-3 MPH. However the reality is that I really  dont know what I should expect. With a 5.7 engine and duo prop drive with SS blades, I was hoping for more than 44 mph. I didn't buy this boat to break any records, but for more comfort and cruising, however when I want it to go, I would like it to go a speed that would at least match the very cool sound of the exhaust.

 

Thanks for helping me.

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 Hi!

 What model engine is it? 5.7 liters can vary in power from 280 to 320hp. I found this doc after a quick search. 

http://forum.chaparralboats.com/publications/Editorials/04mag/04-256SSi_SmoothAsTheyCome-GoBoating.pdf  The last page may be helpful to you. 

Keep in mind a full tank of gas (70 gal) is about 420lbs, so that with 3 people is not the ideal top speed testing weight.

Dings and dents definitely could be the reason you are not getting your projected speed. If we were talking 10 mph difference I would say no, but a 3-4 mph difference definitely can have to do with imperfections of the prop.

Depending on the exact model of your engine, the max rpm can vary, however, it should be in the ballpark of 4500-5000 rpm in my opinion. Exceeding 5000 would not be good, so you seem to be at a fine place as far as rpms. Maybe you could even move up bit pitch wise if you want more top end speed. Moving up an inch in pitch typically will lower the rpms by about 200rpm.

I know nothing about duo props

 

P.S Next time post in "Boat Talk" More people will see it that way

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Thanks for the info. I have the 320 horse Volvo. From the article looks like I really don't need to search for more speed. Irregardless it's an amazing and very comfortable boat. It has what we need so I'm good without the 2-3 mph. 

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Ok!  As I said, you could increase your prop pitch to get the few extra mph. But it sounds like you are happy so might as well leave it! Also forgot to mention, you shouldn't need to trim halfway up to get the Rpms to rose at WOT. Halfway up seems like a bit much to me. 

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