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Old 05-23-2015, 12:09 AM   #21
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Effectively retro-fitting a later manufacturer modification is more likely to rectify than create problems.
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Old 05-23-2015, 12:27 AM   #22
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I would seriously doubt much if any stiffness issues where created and IMO if any deflection was imparted into the hull stringers it would have immediately manifest itself as prop shaft vibration.

All in all it was a painfully cheap and easy fabrication job. Less than 1 hour shop time and all material(except Al's hardware, paint and felt) was literally pulled out of the scrap metal bin.
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Old 05-23-2015, 06:43 AM   #23
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Ok, thanks for the replies...Like I said, I was just curious. Since rigidity in a sky scraper makes them vulnerable to earthquakes, I was just thinking that since a boat is effectively in an "earthquake" all the time, excess rigidity could be a problem.
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Old 05-23-2015, 10:07 AM   #24
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Good question and point wyoboater,

Rigidity in structures is an age old question and as you point out there are structures where flexibility is a good thing .. not bad. But even in your skyscraper example the goodness of flexibility is very limited.
It was said in the old days that flexibility was good when traditional wood and canvas canoes were starting to be replaced by canoes built of other materials. The old school paddlers and builders said a canoe paddles better when the bottom is allowed to flex between paddle strokes. Garbage talk IMO.

Most of the time flexing of structures is good only when it flexes instead of breaking .. as in the case of the skyscraper. If an earthquake was continuous a building would fail very soon but fortunately earthquakes only happen for very few minutes or more often only a few moments. So in this example designed-in flexibility is good.

The advantage of flexing is that at times it softens a force .. allows it to be applied over more time so the amplitude of the force is reduced. But the power of the force is not reduced. If you were to take a fairly sharp stick and push me out of the way by applying force to my body for several seconds I may not be damaged. But if the same force was applied w the same stick in one 50th of the time very serious damage to my body would probably result.

In a wood planked boat often forces are absorbed by allowing some small amount of movement. But over time that movement causes damage. Sheer loads are applied to sealers and caulking and eventually serious breakdown occurs. Fasteners like bolts and screws are installed in tight fitting holes and are very strong but over time and flexing from shock loads or just slowly working will crush or wear the holes larger and some strength will be lost and the same "working" will have wider limits. Eventually the boat will "wear out" .. it will become so flexible that failure of individual parts will render the boat unsafe. Refastening or/and rebuilding will restore much of the boats strength but she will never be as strong and durable as when new.

Different materials respond to flexing in very different ways. Wood props are great on airplanes as the wood flexes so gracefully it can absorb millions of cycles of flexing. But only along the blade .. not at the hub or it would become loose from it's mounting.

Re the OP the floor in the original boat was/is free to move up and down a small amount as it is attached to the sides and decks of the hull. And the hulls flexing is limited only by its bottom structures like the longitudinal stringers. When we add the struts as in the OP the flexing of the floors is greatly reduced as the weight of the floors and everything on them is now applied to the bottom not through the sides of the boat but directly to the bottom and the sea .. through the struts.

My own opinion is that some undesirable flexing on the outboard areas of the floor is greatly reduced and the bottom will (to a great extent) have reduced flexing as the load from above is applied directly to the part of the bottom most likely to flex.

Looks like a win win situation to me and the boat is better off w the struts than w/o. Just a theory of course and anybody is welcome to blow me and my theory out of the water. I think it's a good modification. Some transfer of engine vibration applied to the hull bottom would be transferred to the floor above and to the feet of those standing on it through the struts. If the struts were solidly attached some reduction in hull vibration would result from the load and mass on the floor being added to the total mass the vibrator (the engine) had to work on. But people don't stand on the hull of trawlers .. they stand on the floor. But the original intent was to keep the floor from sagging and that part of the mod is 100% good IMO. Whether to soft attach or hard attach the struts is another question .. IMO.
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Old 05-23-2015, 10:29 AM   #25
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IMHO - If a pleasure boat's stringers and/or hull integrity becomes too jeopardized by simple floor supports intended to limit/stop floor creaking... then the boat was not built sturdy enough and should be scraped; before some other instance of stress sinks her and endangers lives..


BTW, and as an aside: In regard to Eric's mention of building flex in earthquakes...


In areas having too often advent of earthquakes it is best to have many of main structural components attached by Hot Dipped galvanized nails in applicable d size. And, not with screws that are so often used in today's fast paced (make it quick/easy) home building market. Reason - HD galvy nails offer considerable (the best general fastener) flexing capability before fatigue could break them. Screws are ridged and snap with little to no flex capability. A mix of both type fasteners can also provide good results for many reasons during building.
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Old 05-23-2015, 02:31 PM   #26
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Screws are probably higher carbon steel or stronger for some other reason. If you had a nail long enough you could probably tie a knot w it. In an earthquake nails could pull half of the way out and then still be holding something together. But the house could be a twisted mangled mess.

Aircraft bolts are not as strong as many bolts found on cars. But if put in a vise a hammer won't break it. They just bend. That ability to bend and not break could keep an airplane from falling out of the sky.

Screws in building houses? Never even heard of screws in houses except for hanging doors.

My boat had a sagging afterdeck problem and I hope you don't think I should have scraped it. Never entered my mind. And I don't think it occurred to Craig or FlyWright.
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Old 05-23-2015, 06:35 PM   #27
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Ok Eric, thanks for the explanation...what I've actually gotten out of it is that the engineering side of boat building AND earthquake proof building design is incredibly complex and better left to engineers than laymen like myself. As I stated in my original question, I was in no way criticizing the repair, in fact, I think it's ingenious!. It just brought that question of rigidity to mind and I knew if I asked it here on the Forum, I'd get an explanation. I now understand better than I did, so again, thanks!
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Old 05-26-2015, 03:03 AM   #28
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Good question and point wyoboater,

Looks like a win win situation to me and the boat is better off w the struts than w/o. Just a theory of course and anybody is welcome to blow me and my theory out of the water. I think it's a good modification. Some transfer of engine vibration applied to the hull bottom would be transferred to the floor above and to the feet of those standing on it through the struts. If the struts were solidly attached some reduction in hull vibration would result from the load and mass on the floor being added to the total mass the vibrator (the engine) had to work on. But people don't stand on the hull of trawlers .. they stand on the floor. But the original intent was to keep the floor from sagging and that part of the mod is 100% good IMO. Whether to soft attach or hard attach the struts is another question .. IMO.
My experience bracing up my salon floor was consistent with your theory. Californian built a box floor system without solid horizontal floor joists side-to-side and no vertical bracing. This allowed for two large removable floor sections for engine removal and major maintenance access. As you point out overtime everything loosens up and now you have floor sag.
Adding additional bracing did indeed restore the level and rigidity of the floor. But I noted that one of the vertical braces I added between the main stringer and the floor joist (and just a few inches ahead of the starboard engine mount), transferred an unbelievable amount of engine vibration and noise to the salon floor, to the extent I finally removed it. Unfortunately it's the ideal brace location to plumb the floor. Until I come up with a shock absorbing mount I can live without it though.
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Old 05-26-2015, 12:44 PM   #29
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Interesting analysis, Larry. I added one exactly where you describe and kind of figured that was the one most likely to be transferring the vibrations to the lower helm floor. It's also the one that raises that corner enough to clear the coolant cap.

I had not thought of removing it but maybe that's the best solution. I'll try releasing the jack a bit to see if it reduces the vibes.
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Old 05-26-2015, 01:49 PM   #30
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Why not attenuate the vibrations?

http://m.grainger.com/mobile/product...Isolator-2NPD9

Just one example.
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Old 05-26-2015, 06:39 PM   #31
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To address the vibration, would it be possible to reinforce the floor joints while the floor is jacked up into position, then remove the jacks and let the new joists carry the floor with load bearing down out at the sides of the hull as originally designed? It's clearly more work, but might be worth it in the long run. Or would that be logistically impossible?
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Old 05-26-2015, 08:08 PM   #32
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Is incorporating an engine mount feasible? It is a "well invented/perfected wheel",if they can support a vibrating engine they should support a deck. Lots available, auto and marine, must be one which adapts to the task.
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Old 05-26-2015, 08:52 PM   #33
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To address the vibration, would it be possible to reinforce the floor joints while the floor is jacked up into position, then remove the jacks and let the new joists carry the floor with load bearing down out at the sides of the hull as originally designed? It's clearly more work, but might be worth it in the long run. Or would that be logistically impossible?
I don't have the skills, dollars or inclination to tackle a job like this. The "issue" does not even approach the severity required to replace structural members. I think the level of vibration has magnified through the internet beyond its actual level.

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Is incorporating an engine mount feasible? It is a "well invented/perfected wheel",if they can support a vibrating engine they should support a deck. Lots available, auto and marine, must be one which adapts to the task.
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Great thoughts. Might consider it if the Admiral objects to the boat's vibes. Who knows...she just might like it!
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Old 05-26-2015, 09:21 PM   #34
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Might consider it if the Admiral objects to the boat's vibes. Who knows...she just might like it!
OTDE just could be just around the corner...


OMG - Read the first paragraph in Eric's post #35 below... obviously regarding your statement quoted above . "Lacks stiffness", "move up and down (vibrate)", "stiff rod is put vertically"! Plainly OTDE type o' stuff - LOL
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Old 05-26-2015, 09:32 PM   #35
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If The boat lacks stiffness in it's hull bottom the engine will make the bottom move up and down (vibrate) and if a stiff rod is put vertically between the floor and the bottom the vibration of the engine and bottom will be felt on the floor. Not rocket stuff.

The original problem was floor sagging but now it seems to be floor vibration. Since floor stiffness isn't an issue a spring loaded rod should almost eliminate the vibration. Rubber pads may be simple but will probably only reduce vibration a small amount and could even amplify the vibes if there was resonance involved. The longer the spring the better but a small car valve spring could provide a workable load. A scale to determine the load necessary to put the floor in the right position would probably be a good place to start. Then considering the number of rods and the the force of each rod should dictate a place to start w a single rod. A "U" (cup) like holder overhead and on the top of the rod could contain the spring. Nested over and under each other.

A long shot would be to bolt the rods as solidly to the lower stringers and the floor beams. Feel the stringers while the boat is underway and if the vibration is slight rigid mounting could help. If the rods are not solidly attached together the boat bottom and stringers could act like a jackhammer pounding on the floor bottom. As the bottom, stringers come up the rod forces the floor up. Then the stringer moves down. If the floor is not firmly attached to the rod and the rod is firmly attached to the stringers when the stringers go down a space will develop between the floor and the top of the rod. In another instant the stringers and rods will violently move up likely when the floor is coming down. Really severe vibration could be felt on the floor if this is the case.

Just some thoughts.
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Old 05-26-2015, 11:18 PM   #36
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Old 05-27-2015, 01:37 AM   #37
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To address the vibration, would it be possible to reinforce the floor joints while the floor is jacked up into position, then remove the jacks and let the new joists carry the floor with load bearing down out at the sides of the hull as originally designed? It's clearly more work, but might be worth it in the long run. Or would that be logistically impossible?
I believe anything is possible, but time, effort and cost are all considerations. I've seen examples of horizontal bracing with metal beams that seem to work just fine. But do I want to go to that much trouble, probably not. In my case, the ideal location for plumbing the whole floor is two inches ahead of a motor mount. I suspect the proximity to the mount is the problem. None of the others support posts I added cause this problem. I think some type of attenuation mount is possible or just rethinking the bracing scheme. When I return from Spain next month, I will have some time to play with it. Maybe there is a simple solution.
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Old 05-27-2015, 09:10 AM   #38
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Edelweiss,
I thought this was Al's (FlyWright's) problem. You have the same problem too?
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Old 05-27-2015, 11:47 AM   #39
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The sag is a common issue with Californians and several of us have added supports to cure the sag.
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Old 05-27-2015, 12:38 PM   #40
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I think the little rubber doohickeys will just crush and run out of availible movement. Unless they were really big. Springs can compress all the way too and if that happened the vibration would really be terrible. But if loaded a little less than half way methinks they would be perfect.

Has anyone mounted them hard? Not just stuck in there. I mean like bolted.

By the way really weird things are appearing on the thread. The pic of Kevin's anchor is appearing over and over on all the posts. The text is compressed on the right and the pic is in a strange place. Is it my pad or the TF Site?
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