Transom Reinforcement

The outer hull looks good. but if you took off the bracket, you may be surprised.

Just keep in mind, when you put reinforcement in, depending how you transfer these forces, the force has to go somewhere. try to transfer it over a larger area.

I mean not just enforcement, but at the end of the reinforcement.

I know of people who did this, and then there where cracks around the reinforcement.

Plus you don't want to add too much, where you have a lot of weight in the transom.

When I had my shop, I had a customer that wanted to put a 6' swim platform behind his boat. (Big boat)

When he was explaining what he wanted, the weight was just adding up. I did convince him of putting a smaller 4' platform on. I told him even then you'll need trim to keep it level, plus I'm sure there's going to be other surprises.

All was pretty good... I guess, I did see him at the end of the summer and I ask him about it. he did say there was just one issue. I asked him what it was, and he said when he stopped quick, the wake came in and washed through the boat.

Thanks. The hull is not cored, so there shouldn't be rot or delamination. It's complete 1970 fiberglass! I will replace the hardware when I do this in a few weeks, and metal brackets would certainly be lighter.

"I mean not just enforcement, but at the end of the reinforcement."

Could you explain further?

ahhhh... this is from hindsight that I'll share with you.

When I worked at the shipyard, a friend of mine had an older boat. and he was putting on a larger motor on it... a really larger motor. This guy was pretty knowledgable, he actually repaired props as a sideline job.

We were teasing him that that'll tear the transom off. so he reinforced it where the motor mounted.

Well from what I understood, it cracked around his reinforcement. If he would have reinforce the transom all the way to the port and starboard side, it may have worked out. But it was a small boat, so he didn't have much to work with and the motor was way over sized. The side probably would have cracked. I wish it was filmed.

With yours, it may not be too much of a problem, your going back to a smaller motor, and even though there may be a question with integrity. it's nothing that gelcoat and fiberglass can't repair. But something's, when you dig in, one finds surprises. In his case, it turned out the plywood was rotten.

One thing you can't see is the condition of the plywood interior....it could be rotten....I would grind down the crack to see how deep it goes and check condition of wood interior section...Once the crack is ground down to the wood you can refiberglass the damaged area, or if the wood is rotten, replace the transom....

https://www.youtube.com/watch?v=b5D_AhfvLXE

No coring! All fiberglass, thank god!

yes, what Del said....

I like this better than a mechanical brace actually. I can still epoxy the crack and then add fiberglass over it. I can certainly do that along the right and bottom edges of the crack, but you can see along the left crack area it is impossible to reach farther than few inches.

This looks like it is pushed in at the bottom....I think I might consider adding a brace at the bottom....

Usual disclaimer - I am not an engineer. What I see, though, is a motor mount applying a force to the centre of a flat plate, the transom. That force is then transmitted to the sides of the vessel via the edges of that flat plate. If you propose a brace, I propose at least two braces, extending the full width of the transom.

I'll add this, though it may already be in your plans.

Remove all the gel coat with a disk sander and get down to the bare glass fibers, so the resin/epoxy can impregnate that as well.

I'd also use glass mat/woven roving instead of just cloth.

The choice of plates is up to you, but stress distribution is the goal.

Good luck.

Sometimes I think I'd like to get another boat. Then reality rears its ugly head.

A boat is just a hole in the water to put your money in.

That's what I have friends that have boats.

BOAT is an acronym: Break Out Another Thousand

I have to remember that and tell that to my BOAT owning friends.... AFTER they drop me off on the shore...

The two happiest days in a flat owner's life. The day he gets it and the day he sells it.

I've heard that one.

Ask me in a year, after a winter of projects and a summer on the water, if that's still true!

hey,.. ahhhh friend.... let me know when your taking her out..

Indeed. It's tough to a get a grinder or disk sander down into the area, so an orbital will hopefully do. I don't expect gelcoat on this side of the hull.

Once I get more area exposed and can judge the the depth of the crack a little better, I will consider some bracing hardware. If it is just surface cracking, like I expect (and hope, lol), then some cloth and a few layers of epoxy and hardener should do.

That sounds good....

Please.... do not use epoxy until you know what the actual base plastic is. Is it poly, vinyl, epoxy or other?

I have built with all and they will not work well together unless you know to what they are being joined. In many cases where two resins are being used, micro hairs and micro fibers are applied, sometimes in the resin and other times applied directly to the surface after wetting.

It is not brain surgery but does require more understanding than sand and coat.

Merely roughing a surface and adding resin is a disaster in the making that any course at a community college or good book can help when dealing with two part plastic reinforced e glass, s glass, kevlar, carbon or other cloth. Certain types of cloth are pretreated to absorb the resin and are resin specific.

All of this is easily found on the boat blogs. I would recommend a bit of library work that would revolve around a few of the points put forward.

I have seen first hand the results of a great job finished handsomely with good paint... fail.

Metering, weighing and measuring correctly to include temperature and humidity, are key also.

Take your time, learn a lot and most of all have fun 'messing about in boats'.

At the risk of creating another "I know more than you do" controversy, it is a pretty good bet that the boat is built using "glass" fiber and polyester resin. Determining the type of glass would require a lab analysis. Carbon (black) or Kevlar (yellow) is only used in high performance boats, which this is not.

While polyester resin would be the same family as the parent resin, and fine for the job, I don't think marine epoxy would be a bad choice as a patch.

While I defer to your boat building prowess, I spent many years as a materials engineer with an aerospace/military electronics manufacturer.

Hush should continue as he has planned.

I would be willing to bet a princely sum that it is a polyester resin with regular old 'glass' as well. I've been around boats my entire life as my parents were avid sailors.

I would do some light grinding to get down to 'virgin' material free of paint, dirt and oxidized resins, clean it really well and that way the solvents in the repair resin can help create solvent welds between the old resin and the new.

Framers timber chisel

..

What we used on old, badly glasses reinforced areas

I agree with what the others have said, but I'd add two small comments. 1. Be sure to round-off the corners of whatever reinforcement you use. Sharp corners are stress risers, so you want to avoid sharp corners. And 2. You might want to add some vibration-damping grommets under the motor mount surfaces. You can google the term to find what kind would work best.

From the engine size and picture of the transom I am going to guess this is a sailboat under 20ft?
Don't forget to check where the transom attaches to the sides and bottom for cracks, if there are stress cracks at the motor mount there might be some at the edges too. Although I would guess from the pictures that the boat impacted a pier or something with the engine. It just looks like a shunt as opposed to fatigue.

Drew K

1970 Matilda 20'

I had a Coronado 25 for a bit, but that experiment failed :-/

But the research rekindled a passion for a floating home! Someday....someday.

Drew K

Thankfully the boat is structurally sound, good sails, decent outboard and excellent trailer. There are a handful of laborsome projects that need to be done, and about a dozen smaller projects that should be done before its launched again.

Look for upcoming blogs that depict this project in greater detail.

My advice would be to enlarge the outside surface area of the mount,perhaps even doubling the length of the mount to,distribute the forces,and as noted elsewhere,use rounded corners at all contact points.

Sharp points and corners amplify forces,aka:stress risers.

If you simply repair the existing area,you will still be applying your load to an existing flexible area,which could create stress risers within the old fault lines,unless you grind the fault lines out totally.

If you don't get rid of the old cracks,or use the same size mount,there will always be a weak spot.

Of course,you could simply pile multiple layers of fiberglass mat and epoxy and hope for the best.

However,the ocean is not a good place to discover your mistakes.

Also,I agree with adding vibration mounts to the motor,as mentioned by others.

This is in addition to the inside reinforcements recommended by others.

Good luck.

For you, BOAT means Break Out Another Ten-thousand.

BOATT

It keeps me busy, that's for sure, but there is a wonderful quote, versed by Water Rat, in the book, "Wind in the Willows", by Kenneth Grahame that goes :

"Believe me my young friend, there is nothing, absolutely nothing- half so much worth doing as simply messing about in boats..."

That also pretty much sums it up for me.. Others like to go to Vegas and part with their hard earned wages...

Oh, I know it well.

My gimbal bearing went bad on my 1992 Wellcraft bowrider because the outdrive U-joint bellows developed a tear and unbeknownst to me the bearing was being bathed in water. Pulled the outdrive, replaced the bearing, seals, the exhaust bellows, U-joint bellows, and the tilt sensors/wiring . While trying to re-install the outdrive, I noted that the drive shaft didn’t want to slide back into the engine coupler. Went to re-adjust the motor mounts to re-align the shaft and noticed my motor mounts were sagging at least half an inch. I built a 12 foot high set of gallows in the driveway and yanked the engine.

The original motor mounts were boxes built using ¾ inch plywood that was then glassed over with maybe two plies of fiberglass. But unfortunately, there were no drain holes at the bottom of these glassed-over plywood boxes. So yes, after 22 years, water gets in, doesn’t get out very well and the predictable thing happened. I cut away the glass and scooped out the rotten wood remnants. The engine was only being supported by the two plies of glass and eventually it sheared and dropped.

I left about ¾ inch high outline of the glass wall to help hold the new motor mounts. The new mounts were formed by gluing together four sections of carefully cut pressure-treated 4 x 4’s and topped with a ripped down 2x8. These solid motor mounts were coated with polyester resin and bonded in place. They will outlive the rest of the boat I am certain. I lightly ground and then thoroughly cleaned the glass where I would be bonding the mounts and adding new glass.

A couple of plies of glass around the edges to hold the mounts in place, some angle brackets, and 8 inch long timber bolts hold the mounts to the bulkhead. Taking lots of measurements before ripping out the old mounts, carefully cutting the angles, and test fitting before bonding all paid off. I dropped the engine down on the new mounts and the height was perfect. I aligned the engine side to side and front to rear, then marked the holes for the engine mounts and lifted the engine back out. I drilled the holes for lag bolts of the engine mounts and set the engine back down on the mounts. I did not have to adjust the threaded mounts on the engine in the least. The drive shaft just slid right back in. I’m really glad I didn’t have to futz around with those hydraulic engine mounts, threaded adjusters and locking tab washers in tight quarters. Finished just in time to put her up for the 2014 season. Oh, well.

I see you love boating due to its relaxing nature.

When I am actually using it, yes.

Maybe you should take the day off and go golfing... I hear that's quite relaxing.

Is that a kitty cat milk plate in the lower left of the picture ?

I think I probably brought my sandwiches out to eat while I was contemplating my next action. (I too was trying to remember why I had a paper plate out there. )

The thing I am not seeing is exactly how the motor mount is constructed.

1. Are there 4 studs attached to a large metal plate that is sandwiched between layers of fiberglass ?

And if there is a plate, what type of metal is it.

Or

2. Are there 4 separate studs that are embedded in layers of fiberglass ?

And are the studs connected to " feet ".

Depending on the construction of the " mount " , this can give you several different options for your repair procedure.

I owned my own business for a few years, a marine repair shop. I suggest that you remove the gill bracket and poke around in all four of the bolt holes in the transom. You are most likely to find that there is a piece of wood in there that was glassed into the inside of the transom for additional strength in mounting the gill bracket. I have run into this issue many times. If the manufacturer had actually constructed the hull out of 100% fiberglass, then there would have been no cracking/delamination inside the transom in the manner shown in the photos. Maybe I'm wrong but it can't hurt to get into those bolt holes and see what is in there.

GA! The bolts go through the hull and the mounting plate (wooden block on the inside of the hull. Can not see if there is a metal plate there too but best to ASS-U-ME that there isn't one. When the motor bracket is installed the hole pattern of the bracket bolts are drill through everything. The bolts used may have a head similar to a carriage bolt so they don't turn while in the bracket. Of course only 304 or 316 SS for fresh water and only 316 for salt water should be used. One reason for all this is that not all motor brackets have the same mounting bolt locations, patterns and sizes. As the author stated the previous motor was oversized for the boat. That is what caused the glass failure. Purchasers should believe the manufacturer's recommended maximum HP.

Wood is sometimes used so that the backing plate has some compressibility to dampen some of the vibrations. If so, oak or mahogany should be used not a soft wood such as poplar or pine. As I detailed in #40 it is best if all the assembly and glassing is done at the same time. There is more strength that way. Similar backing plates are used for deck cleats, chocks, winches, lights, tender tie-down fixtures, etc. If at all possible bolts/screws are used to mount the fixture to the plate with through-holes and not wood screws (just as the motor bracket is held in place).

All of this is pertinent to small to medium length sailboats, up to 50-60ft loa. Some examples of commercial backing plates are:

http://greatlakesskipper.com/boat-parts/building-materials-maintenance/backing-and-support-plates

http://www.sailnet.com/forums/gear-maintenance/100607-mooring-cleat-backing-plate-installation.html

A few years ago I rebuilt an older model O'day 17ft Daysailer with a nephew and I insisted that we replace all the backing plates. He thanked me last year because of what he had seen of others that didn't, especially during storms.

Good Luck, Old Salt

The bolts go all the way through the internal backing plates, through the fiberglass, and through the aft transom plate. Rather than 304 ( stronger than 316, but also more apt to corrode), stainless, use bolts with F593C stamped on the head, much stronger, and as corrosion resistant as 316 grade. We then use a stainless washer over the motor mounting hole, to spread the nut load a bit. We use longer bolts to allow double nutting, rather than nyloc nuts or Loctite.. Locks them much better. See if the motor manufacturer designates any torque requirements. Do not over tighten so as to not preload the bolts, then add the second nut to complete the assembly. We leave 3 full threads showing past the locking nut. Good luck!

Didn't go into that much detail but most of what you stated I agree with. I don't agree about the necessity for the F593 instead of 316SS bolts. Yes, 304 is not suitable if boat is used in salt water. 316 is much better and has better corrosion resistance. The corrosion presents itself as "worm holes" in the metal over a very long time in salt water. If the approx. 20% greater strength of F593 is a determining factor then you should be using a larger bolt to have a bigger margin of safety.

I have a 20ft wooden sloop with a "spartan" cabin (two bunks, a head, some electronics and not much else). We made it and the boat is 50 yeas old and still going strong. All fittings and hardware have been changes to SS from brass and bronze over the years. All running rigging is mostly 316 SS. The center board and the bolt it pivots on are 316ss. There is absolutely no sign of corrosion on either of them when examined with a magnifying glass. They are in salt water 24/7 for over 6 month/year. 316 was certainly the right choice. Nothing on the boat that is 316 has ever shown any signs of wear or corrosion.

Good Luck, Old Salt

Good work on your boat ! Sounds like a beauty, and sounds like it was put together with love and precision. Re: stainless grades. F593c is a version of 316 stainless, just a higher strength alloy--We use it as 500 lb motors are being cantilevered 14 inches off the transom with jack plates. Also, those are the standard grade specified by Yamaha and T+H Marine for all their outboard motors and transom mounting brackets. There are some even more exotic alloys, like 17-4, but are overkill. As an aside, when working on Navy wooden minesweepers (When magnetic mines were still prevalent, altho in 3rd World, they are still used.), we found all the wood screws to be of a high grade of Monel. They all came out looking brand new, even after 30 years. Nice if you can afford them. One other thing...I have found some of the sites advertising 316 and other grades of stainless to be suspect, especially if ordered through overseas (think China, Malaysia etc.). Had cleats go south in a matter of months, in regular boatyard air, not even in the water..Various amounts of pitting. Know your supplier !

I definitely plan on taking the original hardware out for inspection/replacement. I'm 95% sure that the boat is all fiberglass. It's an early fiberglass boat, and I went over the entire boat tapping w/ a screwdriver handle to check for delamination.

It is totally possible that there is a core in the transom. The repair, when it occurs, will be covered in a new blog series starting on CR4 this week!

I think he was saying there might be a block of wood, not a total core in the transom. Poking around with a scribe or small screwdriver wouldn't be a bad idea. How about some pictrures of the rest of the boat? I wouldnt mind seeing pictures of the spartan 20' wood lady mentioned earlier also.

Drew K <--- is missing the water

Look for a blog post tomorrow!

After the variety of 50 responses for this post, aren't you glad it is a smaller auxiliary sailboat and not a 12 meter or a J-Boat? Maybe not though, they don't have engines so there is no mounting plate as part of the transom.

Good Luck, Old Salt

P.S. When grinding and sanding the fiberglass, PLEASE wear a quality respirator for fine dusts. An MSA respirator can be bought from the big box home stores for less than $40.

A regular dust mask is not enough. Tight fitting goggles are highly recommended as well.

The absolutely first part of the repair that you need to do is "enlarge the backing plate/block where the motor bracket is mounted on the transom. That is the rectangle where the four mounting bolts of the bracket go through the thicker part of the transom. The crack was formed by too much vibration and force from the motor. The faster the motor is run the more stress is put on the top and bottom than on the sides of the plate. This is a common deficiency on fiberglass boat transoms and engine mountings. If I designed your boat I would have made it with a backing plate/block at least twice as big as the one you have.

The thing that enables you to mount running and docking gear to a thin hull or deck is the backing plate/block mounted behind the fixture. It holds the longer screws and distributes the force over a wider area.

If it were my boat, I presume about the size of a Lighting or shorter 20's foot I would first clean up any stray cloth or epoxy "strings" so you have a smother area to glass to. Next I would take a piece of Mahogany marine plywood the same thickness as the depth of the present backing plate, cut it at least twice as big as the current backing plate. Cut a hole in it just bigger than the current mounting plate. With glass and epoxy mount this around the backing plate. As soon as the new backing block is in place, and well before the epoxy hardens, drill holes through the effected area. Use only 304 or 316 Stainless with fender washers. The washers and heads of the bolts will be on the outside of the transom. Take a piece of 3/16" Stainless plate the size of the mahogany and drill holes in it for the previously install bolts and the old bolts. Tighten up all the bolts and let it harden.

The bolts and fender washers on the transom will not be unsightly. They will probably be noticed by only you.

Auxiliary powered sailboats usually have displacement hulls and not planing hulls. Once the maximum speed has been obtained the excessive hp starts to put stresses on the boat, especially the transom. With a planing hull this simply raises the boat more and make it go faster.

In summary, you have fixed the crack, reinforced the backing block for the motor bracket, reinforced the transom, increased the value of the boat and got back on the water. This repair will make the boat like it should have been designed years before. I have seen too many boats with major damage to the transoms that have been relegated to the grave yard due to too much hp.

Good Luck, Old Salt

GREAT reply. I need to clean out and sand the area down before I can really assess the total deformation of the location. It's located in a lazarette, so I'm a bit hampered by accessibility and working space.

Right now, my options are (assuming I don't need to recore):

1. Smallish, surface crack: Marine epoxy crack, then laminate a layer of mat with marine epoxy, followed by successive layers of fiberglass laminate.

2. Larger crack: Marine epoxy crack and laminate. Cut marine grade wood to size and install to transom. Install backing plate on wood.

Really hoping its option 1, but option 2 isn't so bad either.

Sounds good but, as you mention it is in an area that is very confined, difficult to get into, just beyond your reach, can see what you need to, requires a contortionist with 45" arms and hands that are skinny and strong. Been there, done that and do everything possible to avoid it. The best way I have found is to "overkill" it. Make it better than the minimum while you have this task in process. If for example, it is much easier to put an extra sheet of glass and epoxy on while you have everything apart with the best access also. Think ahead instead of working under duress.

As soon as I find some I will post a picture of my sloop as someone else requested. Its very hard to take "selfies" of a boat underway.

Good Luck, Old Salt