Shaft Bent?

[aweimer]

So i ment to share this when i pulled her out but forgot. While idling in the rack getting winterized my wife notices the shaft wobling. NOT GOOD.

The history here. Hit a log this summer, had both shafts, props and one V-Strut replaced. Then when hauling out find one shaft is bent. I didn't hit anything the rest of the summer either.

Again going to have it worked this spring, stinks! I was thinking though, do you think it could be an alignment issue?

Anyways, thought i would share. Hard to see until its zoomed in. Then the wife pans to the prop.. ugg.. I was up top running the throttles.

Shaft Wobble Video

[farfrompuken]

looks like when they replaced your shaft they might not of aligned your trans,shaft prop and strut correctly

[jon_e_quest]

aweimer... because the boat sits differently when on the hard than when in the water, two separate alignment procedures must be accomplished. The second alignment needs to be done after the boat has settled for a few days at the dock. If you're confident it's an alignment issue, then wait until spring AFTER the boat is launched.

Also, make sure there's no stringer delamination to illiminate that as a possible cause for the mis-alignment. There's an inherent weakness in Tri-Cabs on the outboard stringer just ahead of where the outer v-drive mounting bracket is located. Trojan cut the outer stringer way down to pass beneath the aft head to port and companionway to stb'd. To make matters worse, the portside outboard stringer was cut even more to provide room for the shower drain pump hose where it crosses on it's way to the thru-hull fitting. You'll know you have stringer issues if the bulkheads just forward of the v-drive units are cracked from excessive flexing where they're tabbed to the hull bottom. These bulkheads are just 3/8" thick so the damage will be fairly obvious.

BTW, our Tri-Cabins are pretty old now, we should all be inspecting these areas at the end of every season.

[k9th]

aweimer... because the boat sits differently when on the hard than when in the water, two separate alignment procedures must be accomplished. The second alignment needs to be done after the boat has settled for a few days at the dock. If you're confindent it's an alignment issue, then wait until spring AFTER the boat is launched.

Also, make sure there's no stringer delamination to illiminate that as a possible cause for the mis-alignment. There's an inherent weakness in Tri-Cabs on the outboard stringer just ahead of where the outer v-drive mounting bracket is located. Trojan cut the outer stringer way down to pass beneath the aft head to port and companionway to stb'd. To make matters worse, the portside outboard stringer was cut even more to provide room for the shower drain pump hose where it crosses on it's way to the thru-hull fitting. You'll know you have stringer issues if the bulkheads just forward of the v-drive units are cracked from excessive flexing where they're tabbed to the hull bottom. These bulkheads are just 3/8" thick so the damage will be fairly obvious.

BTW, because our Tri-Cabins are pretty old now, we should all be inspecting these areas at the end of every season.

jon_e_quest -

Is the stringer problem you mention unique to the tri-cabins with the engines under the aft-cabin floor or to all tri-cabins?

[aweimer]

She is wrapped tight, but i will put this on the list to check. I have watched while underway and never seen any movment in the VDrive or Stringers. I have also checked the bolts to the V-Drives, they are all tight. No stringer issues that i can see. I will have to check the base of the wall behind the head, via that access pannel.

[jon_e_quest]

Well, here's my take on it. The stringers in question are cut down to pass beneath the cabin sole of all Tri-Cabins, so it stands to reason that there is an inherent weakness in this area to all of our boats. In fact, the main stringers are also cut down somewhat to pass beneath the shower and cabin sole. Keep in mind that there is no gradually curving transition from where these stringers are cut to their lowest height up to their full height... just a sharp 90 degree cut line where the bulkhead changes from one height to the other. Structurally, a sharp 90 degree inside cut creates a natural weak spot. Unfortunately they're located right where the hull 'works' it's hardest.

Both aft stateroom bulkheads create 'hardspots' on the bottom of the boat right where either end of the cutdown sections terminates. Hardspots are normal in every boat with frames and/or bulkheads, but you can't just cut the stringers to half their height in these spots without adding stress to the surrounding structures. These hardspots in turn cause the boat to flex specifically at these points rather than across longer stretches of stringer forward under the saloon or aft in the stateroom. This flexing becomes more pronounced as the boat 'works' and becomes less 'tight' with age. Structurally speaking, Trojan created a teeter totter under the boat, with everything aft of the main cabin bulkhead flexing up and down (if only slightly) while underway. The added weight of the engines, etc., which is partially carried by the outboard stringers, exacerbates the problem, so one could conclude that it's a bigger issue for first generation Tri-Cabins and early second generation Tri-Cabs (twin beds where the weight of the fuel tanks basically replaces the weight of the earlier boat's engines, etc.).

I have never personally been on a newer Tri-Cabin (queen bed), but these boats likely have smaller outboard stringers all the way to the transom to remain below the cabin sole. This isn't neccessarily a problem because the only significant weight that far aft is from the fuel which is carried primarily over the stronger inboard stringers. Although the second gen boats still have a 'hardspot' under the main bulkhead between the aft cabin and saloon, it's not too big a deal because the engines aren't being supported aft of where the outboard stringers are cut-down.

Have no fear, though, if you've found problems. The stringers can be strenthened by sistering stainless plating to bridge the structural gap. The biggest problem is getting access to the repair area. Metal plating has been used by manufacturers for years to return strength in cut-down areas of stringers and frames. Just wish Trojan had done it.


A pic of the outboard stringer below the aft head where a 3/4" shower pump drain hose crosses over to it's thru-hull fitting. Not much stringer under there!


A shot looking down at the sharp transition of the portside outer stringer at the main cabin bulkhead where it begins it's journey aft under the aft head. You can also see the actual 3/8" main bulkhead to the left of the cut line. Big transition!


Looking to port where the main stringer transitions in height at the main cabin bulkhead. The stringer is at it's full height on the right going forward. And the stringer as it passes under the aft head on the left going aft. The vertical member is a main saloon floor support under the galley. Note the steel plate on the right... not sure that this is OEM.

[alexander38]

Why wouldn't they drill holes in the stringer instead of doing that, that just spells failure .

[k9th]

Thanks for all of the info and the photos Jon (guess that's your name).

I am not one who works on my boat due to my age and physical limitations. Is this something I can have my mechanic check and if so, how easy is it to access these areas? My tri-cabin has a little over 1200 hours on it.

[jon_e_quest]

Thanks for all of the info and the photos Jon (guess that's your name).

I am not one who works on my boat due to my age and physical limitations. Is this something I can have my mechanic check and if so, how easy is it to access these areas? My tri-cabin has a little over 1200 hours on it.

As I said, I've never been aboard a second generation Tri-Cabin. You might be able to see the bottom of the aft bulkhead on either side by simple removing the dresser drawer closest to that bulkhead. And you may have an access 'hatch' in the head sole where you can inspect with a mirror or by taking a carefully aimed photo. Also you can try accessing the stb'd side by looking in the hanging locker. Going down into the engine room is another way to check the main cabin bulkhead.

It seems the port outer stringer is affected more than the stb'd stringer because of the extra cut made to route the shower drain pump line on boats with centrally located shower stalls.

[aweimer]

Thanks again for the info. I will check it out this spring. I honestly don't think this is a problem though. Everything is extremely solid on and around this area. Who knows, worth taking a peek for sure.

I will just have to toss another handfull of money at her and have someone take a look and iron it out.

[aaronbocknek]

Why wouldn't they drill holes in the stringer instead of doing that, that just spells failure .

trojan did some really goofy things when they built boats. honestly, i really do not think they thought that they would be around after 3 or 4 decades. one example is the anchor line pass thru from the rope locker to the deck. instead of putting a watertight seal around the balsa core, they just drilled through the deck and put the pass through on and screwed it to the top layer of fiberglass. the same holds true for the original anchor brace. slapped right onto the deck, screwed into the balsa. i'm sure the bedding compound was not the most sophisticated for its day. this is where most of the deck damage comes from. when dad had our tri cabin hauled out once, the boat yard used a railway instead of the sling lift. the railway was not positioned all the way to the transom and once she cleared the water---B A N G !!! due to the weight of the engines back there, the area was not supported and the hull cracked just behind that stringer. talk about a sick sound. i've never seen dad turn that shade before. it was repaired--- the hull that is, but not sure of any stringer reinforcement. first generation window tracks are also another big problem.

aaron in baltimore

[randyp]

Aaron, I hear ya! The stbd bow deck of our 77 F26 had the same issues - anchor rode hole and anchor chocks, both with no bedding compound, and core rot around that area. Had is "sort of" fixed in 2000 but am contemplating a complete bow deck rehab before launch next spring. Same issue with the hand rails that run over the cabin and hardtop.

[aaronbocknek]

in an effort to understand the stringer issue, i lifted the hatch just in front of the aft double bunk where the sump is located. i poked my head into the area and looked at the stringers, port and starboard. both are full height and look solid. the port stringer has a one inch hole drilled into it so the drain hose for the tub/shower/sink can pass through to the sump system. this is a 'generation 4' tri cabin. from my knowledge this is how the generation sequence follows...

GEN 1. sea raider tri cabin, aft cockpit version, fiberglass hull, wooden
decks and superstructure,engines under back bunks,v-drives.

GEN 2. F-36 tri cabin, all fiberglass hull/superstructure/decks, aft cockpit,engines under aft bunks,v-drives.

GEN 2A(**). F-36 TRI FLY VERSION. aft engines, v-drives.

GEN 3. F-36 tri cabin, no cockpit, flush aft deck, TWIN AFT BUNKS, engines relocated under salon floor, fuel tanks under twin aft bunks, 3 opening port lights, each side, aft stateroom (as opposed to sliding windows)

GEN 4. F-36 tri cabin, no cockpit, flush aft deck, sliding aft stateroom windows, full sized center aft berth, fuel tank underneath.

GEN 5. FINAL PRODUCTION VERSION. island berth forward and aft, flush deck, redesigned command bridge window frame, galley relocated to forward part of salon (u shaped), shorter length of salon windows, one slider each side, screens located on the outside of window frame, redesigned aft head w/ stall shower, no tub, higher aft berth to compensate for larger fuel tank.

hope this helps.

aaron in baltimore

[jon_e_quest]

Aaron... thanks for the information on Tri-Cabin lineage. I never thought in the terms you discussed, but for the purposes of this thread, was thinking in terms of engine layout... early v-drive boats and later straight-drive boats.

Also, the main stringers which you examined on your boat are not so much an issue. It's the cut-down outer stringers, however, that can pose a problem... more so in the early boats because of the drivetrain placement aft of the area in question. It's these cut-down outer stringers and associated bulkheads that should be inspected.