Damaged something underwater - where to start?

chucka · Post by **chucka** » Sat Jun 27, 2009 9:42 pm

I have a Chrysler 318 with a 1:1 velvet Drive transmission in my '75 F26. I put in a new prop shaft 4 years ago, and had the prop reconditioned back to class A specs. I haven't hit anything since then... until today.

I was cruising this afternoon at about 2900 RPM (~ 12 knots) and didn't see a lobster buoy in my path. The engine skipped a beat, the boat hesitated slightly, then continued running at the same speed. I looked back and saw a buoy in the middle of my wake. I throttled back and didn't perceive any noticeable vibration as I continued along, so I gradually brought her back up to speed and continued on about another 20 minutes to Quonset Pt. where I idled around (in fwd or neutral) watching the Blue Angels perform at the RI Air show (great performance!). At some low speeds, (1000 - 1400 rpm) I thought the transmission sounded funny. Not a grinding, not a clunking, I would describe it as a whir at certain RPMs that I wasn't there before. When I increased or decreased speed slightly the sound would disappear. The trip back to my mooring was almost an hour. I ran at about the same speed (2600 - 2900 rpm). During that run, everything seemed OK, until I arrived at my mooring and engaged reverse for the first time. I got a distinct clunking (thump, thump, thump correlated to the engine rpm) from the area of the stuffing box/transmission. I wasn't able to locate the precise source of the sound. When I was on the mooring, I tried reversing the engine a few times, and each time when I went into reverse, I got the clunk which then also occurred in forward. I only engaged forward or reverse for a couple of seconds while on the mooring. I must have damaged something - shaft, prop, strut, transmission?

My question is where to begin figuring out what needs to be fixed? There is nothing there that I haven't worked on before, but I'm not sure how to figure out where the problem is. I'm thinking about starting with an inspection dive to see if there is any visible damage, but if the shaft or prop are slightly bent, I don't expect to be able to detect that visually.

If something were dramatically bent, I think the vibration underway would have been more significant.

Unfortunately, I think this will require hauling the boat. What do you think?

k9th · Post by **k9th** » Sat Jun 27, 2009 10:18 pm

I would think that since it ran OK at 2900 RPM on the way back you don't have a bent prop shaft or you would have noticed that right off. Since the engine skipped a beat as you put it, perhaps you have first fractured a few gear teeth and then stripped on one or both of the gears. That would account for the clunking that you hear especially since it was synchronous with the engine RPM. Since you have a 1:1 ratio you have no real pinion setup where the pinion or drive gear is smaller than the driven gear and thus takes a larger load.

You say that you heard it in reverse first and now in both forward and reverse which is consistent with gear tooth fragments that are fractured and then stripped bouncing around in the gear case. The fact that you can still go both directions adds credence to that since you still have most of the teeth in place and can thus still get movement.

You may have prop damage too so a dive would reveal that. You can probably replace the transmission in the water, and the prop could be replaced but would certainly be easier when hauled out. Hauling out is expensive so that will have a bearing on what you decide.

Just my thoughts. I may be way off base.

RWS · Post by **RWS** » Sat Jun 27, 2009 10:52 pm

if you hit an object with enough force to cause the engine to skip a beat AND damage that trans you better chack the prop, shaft & struts.

Better make sure there is no water intrusion into the hull from a damaged strut mounting.

RWS

prowlersfish · Post by **prowlersfish** » Sun Jun 28, 2009 1:19 am

First of all nothing you said , would make belive there are any damaged gears in you trans .No grears are use when in forward on the 1 to 1 velvet drive . and if a tooth was broke you wound have a constant "ticking " or thump noise in rev only . do you have a ruber type coupler between the trans and the shaft ? if so that could be damaged . I would check the prop and shaft and stut for damage a cracked stut could be a posable cause . anorther posable cause of the clunk is the coupler on the fly wheel may have been damaged .

rossjo · Post by **rossjo** » Sun Jun 28, 2009 9:27 am

Have your diver check it out ASAP ...

I had a completely broken strut that my diver and I replaced this year (in the water). Beacon still has them. My shaft was OK, but the bronze strut was completely broken.

Is it possible you still have line around the shaft or prop? The prop may have cut the line, and left the buoy floating after you passed. You can check quickly with a swim at the stern, where you can see/feel the rudders and probably the prop without having to go completely beneath your boat. You can go under your boat with a snorkel as well ... not fun, but I've done it several times.

captainmaniac · Post by **captainmaniac** » Sun Jun 28, 2009 10:41 am

Line wrapped around shaft would also be the first thing I would check for. As you went over the marker you could have cut the line and gotten a bunch of it wrapped up around the shaft, or wedged in between strut and prop. As long as you were going forward, the 'spin' was still in the same direction. When you hit reverse, some of it could have unwound and re-tangled the your running gear. Cross your fingers - if that's all it is, a sharp knife and a dozen or so dives with mask and snorkel may be all you need to get back up and running.

chucka · Post by **chucka** » Sun Jun 28, 2009 4:41 pm

prowlerfish and captainmaniac seem to have nailed it. I took a dive this afternoon. I had about a foot of rope wrapped around the shaft. I was able to clear it easily. When I reversed the engine, the loose end of the rope is what produced the thump, thump sound. There is no obvious damage to the shaft, strut, prop, or rudder.

The cutlass bearing is now toast. There is no rubber left. I'm sure that the metal on metal of the shaft in the cutlass bearing sleeve produced the whirring sound that developed shortly after I hit the buoy.

After hitting the buoy yesterday, it sounded fine until the rubber in the cutlass bearing burnt up.

Back topside, today, I disconnected the shaft coupling from the transmission and loosening up the stuffing box a little, I was able to slide the shaft back about 3 inches. I went back in the water, to see how the shaft looked where it was rubbing on the metal sleeve of the cutlass bearing. Fortunately, the hardened stainless shaft didn't appear to have any ill effects because the cutlass bearing sleeve is soft brass. I couldn't see or feel any imperfection on the shaft, where it was inside the cutlass bearing.

I ran the engine in both forward and reverse for a while with the shaft coupling disconnected. The transmission sounds fine.

I'm pretty much resigned that I'm going to have to haul the boat to replace the cutlass bearing, but I feel a little better, now that I think the scope of my issue is clearer.

Of course it doesn't make be happy to know that I missed two chances to avoid this expense by a) paying closer attention to avoid lobster buoys, and b) by making sure the prop was clear before getting back underway.

Thanks!
Chuck

PS. Even with my shorty wetsuit, 63 degree water is chilly!

rossjo · Post by **rossjo** » Sun Jun 28, 2009 6:04 pm

Like I said - line on the shaft ... We ran over a line once while we were fishing 50 miles offshore on a weed line with a single screw boat. I had to dive in (amongst the Cudas) and cut the line free to go again.

You can replace the strut in the water, but not the cutlas bearing. You'll have to take the strut off to replace the cutlas bearing. I would line up a shop with a press to do the bearing, and have you diver help you pull the strut, then fill the 4 holes with dowels (and stay behind to watch them while you press the bearing in).

Or you can haul it ...

63deg? I'm envious - 85 deg water here.

randyp · Post by **randyp** » Mon Jun 29, 2009 9:40 pm

Just caught up to this, chucka. I was scrolling down from the top and first thought was "line around the shaft". Glad that was the extent of it, except for the fried cutlass bearing. Same experience on the canal trip last year, but I was going slower and the "line" was a long clump of weeds.

chucka · Post by **chucka** » Mon Jun 29, 2009 9:50 pm

Today I made arrangements to have the boat hauled either Tuesday afternoon or Wednesday. Rather than trying to squeeze the fix into a short haul, I'm going on blocks in the yard over the weekend, so I can replace the bearing at my leisure. It's a bit more expensive than the short haul, but I don't have to coordinate things so precisely, and I'll have time to adapt to anything unexpected. The cutlass bearing should arrive Wednesday. I'll have the prop checked out for any possible distortion while I'm on the hard. I expect to be back in the water early next week.

FYI, the F-26 cutlass bearing specs are 1" shaft diameter x 1-1/4" OD x 4" long.

I'm doing my part to stimulate the economy. Live and learn.
Thanks