Repower 21

[pair of jacks]

By the way- the top end speed I quoted of 31 kts. was with 85 gallons of fuel (out of 95 gal. capacity) and just me on the boat but with all my fishing gear/bags/etc.

AV plate is bone dry (above water) while on plane.

[McGillicuddy]

Originally Posted by pair of jacks

By the way- the top end speed I quoted of 31 kts. was with 85 gallons of fuel (out of 95 gal. capacity) and just me on the boat but with all my fishing gear/bags/etc.

AV plate is bone dry (above water) while on plane.

Your 85 galllons is a lot more weight than the 30 gallons used in the 2 motor tests on the Dusky 203 so comparing your rig to those is not very accurate, and obviously the hulls make it "apples to oranges." Bigshrimpin mentioned the Dusky is smaller than the SeaCraft. The specs had led me to believe it was a littler bigger, so throw my assumption is out the window.

Sounds like you're dialed in on motor height. 31 knots is nearly 36 mph.
I simply thought a 21 SeaCraft hull would out perform the Dusky on the top end.

I posted the 2 tests for capnkid to compare the 2 motors on similar hulls. The test were done 68 and 95 deg temps so that alone would make some maximum performance difference.

Your real world experience with the 21 and 175 etec motor are the best info capnkid could ask for. Your suggestion of a 200 etec makes good sense.

Regarding props - if you make the change, be careful with that bigger blade. I don't know the two props in question, but if you're currently at 5400 rpm, a bigger diameter might set you back.

[pair of jacks]

Ah, the dreaded prop- are you saying that going to the larger diameter prop will reduce rpms? The reason I was considering re-propping is that I've been told by a marina service mgr. and some others that the no-name prop is inferior to the BRP REbel and because of the design of the blades on the BRP that prop will "grip" better thus reducing slip and increasing power- they did not seem to believe that by going from 14 1/2 inch diameter to 15 3/4 would reduce rpm since I'm keeping the same 15 pitch. Now if you guys are telling my otherwise, then reducing rpms is something I'm not wanting to do obviously. Opinions??

[McGillicuddy]

Originally Posted by pair of jacks

Ah, the dreaded prop- are you saying that going to the larger diameter prop will reduce rpms? The reason I was considering re-propping is that I've been told by a marina service mgr. and some others that the no-name prop is inferior to the BRP REbel and because of the design of the blades on the BRP that prop will "grip" better thus reducing slip and increasing power- they did not seem to believe that by going from 14 1/2 inch diameter to 15 3/4 would reduce rpm since I'm keeping the same 15 pitch. Now if you guys are telling my otherwise, then reducing rpms is something I'm not wanting to do obviously. Opinions??

All things being equal, a prop of greater diameter would be harder to turn because it has to displace more water. In turn you get lower rpms.

Being that you are talking about 2 different props of different shapes and maybe materials, it is possible that with less cupping and moderate rake a wider wheel could give you more rpm than what you currently get. There are SO many prop designs.

Svc mgr sounds like a salesman. In theory "better grip, reduces slip" if you have enough power. So it doesn't really increase power, but rather, requires more power as the prop is "holding" more water. "Power" is what you're about 400 rpms short on. If I'm not mistaken, your etec would be be happier if able to get 5800 rpms with your tyipical full load.

Pitch is in theory how far a prop moves in 1 rotation. The prop's cup, rake, & shape and the hull and its power work together to screw up the theory. The result is slip. So pitch is not necessarily interchangeable as svc. mgr suggested.

An 1-1/4" of diameter is significant. I would not drop 500 clams on the marina managers suggestion. Said Rebel might be the perfect prop but if he's so sure, ask him to loan you one.

In general, you need a stern lifting prop that is easy to turn. I don't know specifically the BRP products that offer that attribute, but Bushwacker or someone on the etec board might. PowerTech is making some fine props at very good prices. I would look at the MQS 3 blade ,the SCE and the ELE series. The MQS and SCE are proven stern-lifters. Maybe Bushwacker can offer more insight on the ELE series. Mercury's Mirage plus and Old OMC SSTs also have a strong following among SeaCraft owners on this board.

Looking at the Vipers performance on the Dusky, that might be worth learning more about. Keep in mind that such a performance does not necessarily translate to the SeaCraft hull.