Boat Speed

Ren

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My Seemaste30 (semi displacemet) has currently a top speed of 7.7 Knots, it should do around 11 to 12 knots.
Engine twin diesel 52 Hp each, Max RPM 3000 Crusing RPM 2500.
Props 16 by 13. would re-proping to 17by15 help?
 

duncan

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you seem to be getting displacement performance suggesting that the engines are not able deliver the necessary power to drive throught he resistance hump.
Factors will include (obvious but worth checking...)
weight - how much gear is on board - try emptying the boat onto the dock and seeing the difference
drag - clean hull / stern gear?
Props will make a difference to the charaistics but only if the engines and gearboxes are able to drive them - effected by the above factors heavily when marginal.
and talking marginal - 2 x 52hp driving a boat that must weigh in at over 3 tons (4 ->5?) must be marginal for a semidisplacement - are you sure it's expected to deliver this from these engines? Sounds more in the displacement arena to me.
good luck
 
G

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Are the engines timmable ?
Are the props and hull clean ..... and for props I mean not only from fouling, but also in shape and no turned edges etc.

When measuiring speed are you reading through the water or over ground in a tideway ?
 

Chris_d

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Sounds about right for a 30 year old Seamaster 30, the engines are undoubtly past their best and you probably have ton of accumulated junk on board, plus dirty bottom etc..
I don't think any Seamater 30 does 12knts with these engines, only the original clean bottomed factory fresh boat did that!
I wouldn't waste any money on props or trim tabs, I'm afraid thats as good as it gets!
 

Ren

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Props have been refurbished last winter, bottom is clean antifoulde last winter, speed is trough the water.
Log is accurate.
 
G

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Judging by other posts on this thread .... speed is about right and more is optimistic !
 

Bejasus

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Not totally sure how this works with outdrives, but if I input your boat data into Propkings program, 2 52 hp engines running at max 3000 rpm, as if it was on shafts with a 2:1 reduction, it gives a maximum economical speed of the hull of 8 knots and says that the 16 in prop is too small. Thats taking the LWL as 28 ft, using the full hull width of 11 ft 6 in and a medium cruising ratio for the hull. Seamaster 30 listed as 4 tons at new with 2 ft 8 1/2 in draft. Factory claimed 13 knots at new, although it doesn't say with what engines or drives. According to Propkings, the figure of 7.7 knots looks about right.

"I am the master of my fate: I am the captain of my soul."..........I think????
 
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