Prop Advice?

J

JJRJR

Member
Joined
Jan 1, 2000
RO Number
557
Messages
23
Hey all,

I'm about to close on the purchase of a 1988 Chris-Craft 320 Amerosport. Two things noted in the first survey were:

1) engine RPM rb2@gr5t WOT was 3,700. engines rated at 4,800. only got 22 MPH rb2@gr5t WOT.

2) blisters on the hull

Boat has 2 brand new Marine Power 350's and 2 freshly rebuilt V-drives. I hired a second surveyor to give another opinion on the hull blisters. I read several articles (David Pascoe) that indicated 99% of the time, they are not an issue, just need to sand and repaint. No fiberglass structural damage in MOST cases.

I spoke with the second surveyor this morning and he doesn't think another sea trial is necessary regarding the low RPM's. He said it's very typical for boats of this size to be over propped. Chris-Craft says that boat should cruise rb2@gr5t 22 MPH and top out at 30 MPH rb2@gr5t WOT.

My new surveyor told me that I should be happy to get about 4,200 to 4,300 RPM rb2@gr5t WOT that if I did 4,800 "I'd have no props left." Not sure what that meant, but . . .

So, all that said, what would you expect the props to be on a boat this size, combination? Dry weight is 12,000 lbs, it's got 540 HP, bottom is clean, 12 foot beam and 32 feet long (in the water), inboard motors. Any thought on any of these items folks? Any help appreciated before I sign on the line which is dotted. LOL.

Best,

John
 
What is the gear ratio? What's the Pitch/Dia?

I think 3700 WOT puts way too much load on the engines. Best to do a fresh tune-up before doing WOT checks.
 
Just like Charlie said it is very important to be able to reach WOT with the correct props even though you will not cruise at that rpm. Running overpropped will reduce engine life and running way overpropped will make it happen much sooner. Once you have known good engines in tune the engines need to reach WOT rpm. You say the engines are new but you likely have limited access to the details and install tests so you need to figure out how to prove they are 100% the easiest way for you.
Blisters can be repaired but the area must be completely dry after abrasion before you fill back the imperfections. Normally sand and dry (can take several weeks) then epoxy repair and fair with a glass compatible epoxy, a few coats of interprotect barrier coat and then a few costs of bottom paint.

Hope this helps
 
Thanks guys. I have a receipt for when the props were reconditioned last year that says: 3 Blade Bronze 16 x 14. Also, the v-drive gears are 1.5 : 1

I also sent an email to Chris-Craft to see what the factory recommended prop was on that boat.
 
Chris Craft said that boat came with 16x15 SC Propellers. Something must be wrong if it currently has 16x14 and can't get more than 3700 RPM. Assuming the engines are fine, what else could it be? Bottom is clean. Is it possible the first surveyor didn't trim it up correctly? Recommendation from a prop shop says 16x13 should be the right prop.
 
How much extra weight was in the boat? People, fuel, water and "stuff"?
 
I believe the surveyor, the broker, the owner and maybe the buyer? Not exactly sure. I would be guessing really. Certainly wasn't so much that the engines wouldn't reach the correct WOT I don't think.
 
Yeah, that size prop should easily run the WOT up higher than 3700. At this point, Don't do anything about the prop except maybe have it checked for correct pitch.

Have the V-drive and engine alignment checked...is there any binding?. Something doesn't sound right, like the V-drive has the wrong gear ratio. like maybe the ratio is 1.3 or even lower
 
Now I'm confused. You're the buyer and weren't at the sea trial? A boat can certainly be loaded with enough other stuff including fuel and water that it doesn't reach expected WOT.
 
I live several hundred miles from where the boat is located. I'm having another survey done, so we'll see.
 
The survey I'm speaking of was done by another buyer that lost the deal due to a financing issue, I got a copy of his survey.
 
Personally, I wouldn't be "about to close" until I had my own survey and seatrial done. That's just my opinion though.
 
From the FWIW Department. I have a SR 330 dancer. Roughly the same as your boat. Dry weight 11,500 or so. 1.5:1 v drives mated to 6.2L Merc Horizons. I spin 5000 RPM (Max for that engine) running 16*16, 3 blade props.

I'm thinking if you say some blisters, is there water in the hull?
 
Thanks David, yes that's what I've been driving at and worried about. While your engines are more powerful than the 350's, (I think) this boat should easily cruise at 22 and get top end of nearly 30. My concern is that there is water weight in the hull. Anybody know if a boat can be weighed on the sling coming out of the water? Let's see what my surveyor says, but I do have my concerns.
 
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