Is it a boat or prop problem

[alldodge]

Going to try and condense a year long rebuild and 12 pages of post for hopefully some fresh ideas.
http://forums.iboats.com/forum/engi...mula-27pc-complete-power-plant-rebuild/page12

A single engine Formula 27 foot cruiser with 9 foot beam, drafts 42 inches to bottom outdrive.
Drive ratio 2.0 with Bravo 3, all speeds are GPS readings, tach was checked with computer and is within 50 rpm at WOT

Originally 415HP 502 turning 5200 RPM at WOT doing 46 MPH.
New engine is 530 HP with 3x3 26 pitch prop set WOT 5050RPM doing 46 MPH
Same 530 HP with 4x4 24 pitch prop set WOT 5200 RPM doing 47 MPH

The 4x4 gives best whole shot but prop slip is staying around the 20% mark no matter what is changed. Only thing I cannot verify is the dyno sheet provided to me showed 545 HP (5200 RPM) and 617 TQ (3800 RPM). If I have more HP and more torque why am I unable to get more?

 

[Tail_Gunner]

Bondo's going to the right area here, while nothing is for sure it seems almost certain your fighting bottom paint or the hook. Is the hook on the outer edges of the hull....that could actually be built in tabs i have them on my wellcraft and do not like them but im not going to flatten them out. Your pushing a lot of hull and a lot of weight yes bottom paint could be holding you up make no mistake. Itr's as simple as a orbital two hundred grit and half a days work doesnt take to much to cut that stuff off.

Where's 45 auto this big boat stuff is right down his wheel house so to speak.

 

[alldodge]

Is the hook on the outer edges of the hull....that could actually be built in tabs

Have tabs but their flat even with the edge of the hull. There is a hook about 4 inch wide and goes from the outer edge to about a foot and half inside. Agree bottom paint can cause drag but so can a slick hull, not as much though. That said, push an extra 120 hp and get nothing back out is hard to swallow without some good explanation.

 

[Tail_Gunner]

Well I hate to say this but bottom paint can be a nasty mess Even on small light boats. Another issue is you might not have enough pitch , a bit odd you have duo props upping the pitch and speed and your still at 5200. I pm'd auto hopefully he will chime in.

Laugh's for you...ive been there.

http://forums.iboats.com/forum/gene...nd-topics/633320-turbo-txp-on-a-sport-s-cuddy

 

[Tail_Gunner]

Looked closer you did lose rpm with added pitch (26) @ 5050

Dropped to 24 added two more blades rpm went up speed up .......adding more blade area should have effected rpm to some extent

Aside from bottom paint could there be anything creating a disturbance in the water stream....aka transducer...freshwater pickup....do you have any pic's of the cav plate in relation to the hull???



Originally 415HP 502 turning 5200 RPM at WOT doing 46 MPH.
New engine is 530 HP with 3x3 26 pitch prop set WOT 5050RPM doing 46 MPH
Same 530 HP with 4x4 24 pitch prop set WOT 5200 RPM doing 47 MPH

 

[alldodge]

Had 22% slip with original engine and 24 pitch 3x3. New engine 26% slip with 26 pitch 3x3, then 20% (1 MPH faster) slip with 24 pitch 4x4