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axelkloehn
09-13-2010, 03:17 AM
...had my first ride in the GT21 yesterday with a borrowed 14x23 blackmax (48 78124 23p) on a 260 sbc with bravo one 1:1.5. My x-dimension is about 14".

Symptoms: straight out of the water, gliding with 2000rpm, clean acceleration to 3000rpm, if you try to rev more strong vibration no gain in speed, trimming up helps to a certain point, revs 3500, you push more starts to spin or vibrate again, needs fine trimming to find a certain point- than it revs to 4500 and gains speed...(about 45-50mph)

Any suggestion with which prop I should start trying? I know it is seat time and experience, but may be you guys have tried or can tell me what I should start with. Thanks

Planetwarmer
09-13-2010, 04:14 AM
Is this a new motor and drive? Sounds like a gimble bearing and a prop that is about 2 inches too steep in pitch.

If it is a gimble bearing, hey are super easy to change.

axelkloehn
09-13-2010, 04:30 AM
Is this a new motor and drive? Sounds like a gimble bearing and a prop that is about 2 inches too steep in pitch.

If it is a gimble bearing, hey are super easy to change.

bearing is new. The vibration disappears when you trim down or up a bit. Seems more like it is prop spin from wrong trimming, not depending on the revs. Vibration appears while trimming, you play a bit with gas and trim, it disappears, the prop gets "grip" and it gains speed till wot without any vibration at all. You do this with wrong trimming, it revs till 4500 w/o gaining speed and vibrates, you trim to a certain point which is very difficult to find, vibration disappears and boat gains speed again... is the 21-hull so sensitive or is a prop with 14" too small or others?

Planetwarmer
09-13-2010, 04:38 AM
... is 14" too small?

Funny, I asked my wife the same question before we got married!:kingme:

axelkloehn
09-13-2010, 04:52 AM
Funny, I asked my wife the same question before we got married!:kingme:

well, I saw 2 kiddies jumpin' from your platforms- so I think it worked in your case

BigGrizzly
09-13-2010, 09:26 AM
Prop hub is spinning or the prop is too small a diameter for the bravo drive. thepitch seems fine.

MOP
09-13-2010, 10:04 AM
Sounds like to much pitch to me, my 22C which I believe is lighter and had 300HP ran a 21" 3 blade, which the new engine about 375HP I run a 23 4B. I have a question about the vibration, is there any when you run the engine up in neutral? Can you get the drive to make noise in neutral running it at the dock turning the wheel side to side and or trimming up and down? It probably is the prop but it also could be an alignment issue, was the tool super easy to slide in and out? Phil

axelkloehn
09-13-2010, 02:42 PM
Sounds like to much pitch to me, my 22C which I believe is lighter and had 300HP ran a 21" 3 blade, which the new engine about 375HP I run a 23 4B. I have a question about the vibration, is there any when you run the engine up in neutral? Can you get the drive to make noise in neutral running it at the dock turning the wheel side to side and or trimming up and down? It probably is the prop but it also could be an alignment issue, was the tool super easy to slide in and out? Phil

tool did not slide super easy but with one hand, as far as I remember no specific noises by trimming up and down and turning the wheel l/r in neutral. Hope it is the prop cause it is easier to fix than alignment. I was worried about wrong alignment too cause the tool did not slide as easy as I have been told it should do...