1963 16-footer Project

Repair or modification of Boston Whaler boats, their engines, trailers, and gear
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Rick W
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1963 16-footer Project

Postby Rick W » Tue Oct 08, 2019 9:14 am

I believe I have a 1963 16-foot Boston Whaler. I purchased the boat from the Canadian Coast Guard, Prince Rupert BC. I am told the boat was used, and abused by Canadian Fisheries.

The hull has been modified over the years with a newer seat and console, home-built rail, and windshield. A Yamaha 90 HP was the last engine fitted . The work was done poorly perhaps by a butcher. Someone drilled a 4-inch-hole in the splash well, scooped out a bunch of foam to fits some motor mount bolts, then glued an aluminum plate as a cover. The foam inside was wet when I felt it, and I sucked some water from atop the foam inside.

After removing the seat, console, all the screws, and so on, I flipped over the boat onto some plank stands supported by the boat trailer. I tilted the trailer up and fitted a vacuum to the 4-inch now-upside-down hole in the splash well. I got no moisture out.

upside down small.jpg
Fig. 1. The c.1962 16-foot hull inverted for drying.
upside down small.jpg (74.88 KiB) Viewed 992 times


hole in hull super small.jpg
Fig. 2. The large hole drilled to access the lower engine mounting bolts.
hole in hull super small.jpg (68.51 KiB) Viewed 992 times


Using two bathroom scales and some hydraulic jacks, I weighed one-half of the hull by lifting the two jacks so the supports were coming off the boat trailer. I did three trials with different weights front and back but the totals were all similar, about 310-lbs on average for a half-hull weight. I guestimate the hull at 580-lbs with the support planks subtracted.

The hull looks sound with lots of use but worth bringing back from the edge. My intention is to sand down and re-gel-coat the bottom. I will be seeking advice as i move forward with additional posts. I am thinking to plug the holes with large plywood cut plugs, filling the cavity with 2-lbs-density closed cell foam, and patching the cut hole in the splash well. The foam must be applied in the correct conditions but should be very similar to the original.

Q1: Is the estimate of hull weight at 580-lbs compared to 500 to 550-lbs a concern?
First time owner, long time admirer , purchased a 16ft hull from Canadian Coast Guard. Boat was actually used and abused by Canadian Fisheries. 1963 vintage (I think) will be sharing the progress and seeking advice

jimh
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Re: 1963 16-footer Project

Postby jimh » Tue Oct 08, 2019 10:12 am

A1: I don't think the hull weight is a concern. In 2019 to know the exact original weight of a 1963 Boston Whaler boat at the time it was molded is impossible. If the boat has gained some weight, there is not much that can be done, short of taking extensive steps to dry out the interior foam. A weight gain of 50 to 80-lbs does not seem alarming to me.

Regarding the large hole made through the engine splash well as seen in Figure 2: you should let the transom area dry thoroughly. I cannot imagine the purpose of that hole. There must have been a very odd installation of the engine. When the exposed hull material is dry, make a proper repair.

For repair advice see:

INSTRUCTIONS -- HULL PATCH KITS
http://continuouswave.com/whaler/refere ... tions.html

and

Repairing Hull Damage the Whaler Way
http://continuouswave.com/whaler/refere ... epair.html

Also, the transom has been cut down. The transom was already notched, but it appears someone cut a further deeper notch. This should be carefully inspected and repaired.

For advice on mounting an engine to an older Boston Whaler boat with a shallow sink-type engine splash well, see the FAQ answer at:

Q8: How Does the Engine Mount to the Transom?
http://continuouswave.com/whaler/reference/FAQ/#Q8

jimh
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Re: 1963 16-footer Project

Postby jimh » Tue Oct 08, 2019 10:18 am

Re the boat weight and its static trim: in Figure 1 I can see the remnant anti-fouling paint, which I infer represents the boat's static waterline. I compare this boat's static waterline with the suggested waterline for this hull in the owner's manual. See

Owner's Manual 9 to 17=foot Models
http://continuouswave.com/whaler/refere ... tml#bottom

In the diagram provided by the factory, the water line at the transom is suggested to be from "chine to chine." On that basis, it appears the hull has been sitting with a down-by-the-stern trim. Or, perhaps, the bottom paint was applied generously higher than necessary. If the Yamaha 90 was a four-stroke-power-cycle model, the engine weight may have been higher than anticipated in 1963.

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Rick W
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Re: 1963 16-footer Project

Postby Rick W » Tue Oct 08, 2019 11:04 am

Thanks for the info. The bottom paint does not match the spec dimensions and yes it looks low in the stern to me as well. I believe the last engine was a 2 stroke. I did not notice the notch in the transom. I have no idea how many times the boat has been modified or repowered over its 55 years of service but I suspect more than once.
stearn bolt view small.jpg
Fig. 3.
stearn bolt view small.jpg (77.41 KiB) Viewed 970 times


I removed two lower bolts from inside the 4 inch hole where the foam was removed . I found a bolt hole template in an archive post regarding mounting motors but have not looked too close at that aspect.

I was told the previous motor was a Yamaha 90 and I have the Yamaha 703 remote control for that motor. I cant imagine why all the surgery to mount the outboard. The info I read suggests higher mounting of a Yamaha 90, not lower.

I will look into the notch , thanks for pointing it out

biggiefl
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Re: 1963 16-footer Project

Postby biggiefl » Tue Oct 08, 2019 11:22 am

Put a manual jackplate on it and don't sweat it.

Bottom paint can grow over time as people raise it a hair every year when they paint. Some also do not like the scum line that can go above the paint if moored in more rougher waters and will raise the paint line to cover it.
On my 24th Whaler. Currently in the stable: 86 18' Outrage, 81 13' Sport(original owner), 87 11' Sport, 69 Squall. :roll:

jimh
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Re: 1963 16-footer Project

Postby jimh » Tue Oct 08, 2019 1:00 pm

The modification to the transom made by cutting off about two-inches of the top of the transom at the center should be carefully inspected. The modification has removed some portion of the transom wood reinforcement; that has reduced the strength of the transom. Also, the modification has opened the original laminate structure of the hull at the transom.; that has reduced the strength of the transom. Considering that the boat is 56-years-old, any modification that reduces the strength of the transom should be carefully inspected and repaired.

rtk
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Re: 1963 16-footer Project

Postby rtk » Wed Oct 09, 2019 7:20 am

Here is a photo of the natural "chine to chine" waterline of a 1966 16' Boston Whaler.

1966 16 whaler waterline.jpg
Fig. 4. View of stern showing waterline.
1966 16 whaler waterline.jpg (63.39 KiB) Viewed 929 times


It is not uncommon to bottom paint a waterline quite a bit higher then the water level if you keep a boat in the water for the season on the Toms River. The water is described as brackish and has quite a bit of tannins in it from leaf/organic material decay. It is naturally brown and will cause quite a bit of hull staining well above the waterline.

Install a much heavier engine and add a manual jackplate and the transom will sit a few inches lower then what my photo depicts.

Here is a photo of the original bolt location of the 1966 16' Boston Whaler. The bolt configuration is the blind hole pattern that was used on these boats.

1966 16 whaler blind hole bolt location resized.jpg
Fig. 5. View of transom showing lower mounting bolt position above splash well as recommended.
1966 16 whaler blind hole bolt location resized.jpg (30.67 KiB) Viewed 929 times


The photo you provide seems to show the top mounting bolts quite a bit lower from the top of the transom then the original. The BIA bolt pattern standard puts the centerline of the top bolts two inches down from the top of the transom.

With the top of the transom notched around two inches down and the location of the top bolts I am wondering if someone altered the transom to accommodate a short shaft (15 inch shaft) outboard engine. At the mounting height of the top bolts you depict you may end up with a 15 inch shaft engine low enough to somewhat work.

A CMC manual jackplate works very well to accommodate engine mounting if you do not want to utilize the blind hole bolt pattern.

Rich

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Rick W
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Re: 1963 16-footer Project

Postby Rick W » Wed Oct 09, 2019 8:26 am

Thanks for the pictures [showing a] properly mounted outboard. The two top mounting bolts appear considerably lower on my boat, and that may create another problem.

A 15-inch-shaft outboard very possibly was installed at one point. This old Boston Whaler boat was a work boat.

The console is not original; the bow rail not original; there is a newer seat than original. The boat was likely modified many times of the last 55-years, and there were perhaps several re-powers.

The notch modification looks well done--unlike the butchery from the last outboard install. The engine controls were scabbed onto the console and cables run through the opening in the front of the console where a door used to be,

I have inspected the modification which appears to be well executed with fiberglass reinforcing and no place for air or water to leak in. It may have been done long before the Yamaha 90-HP engine was installed. The work looks to be better quality work than any of the last outboard fitting work. I do not see a potential failure mode due to this modification, and, given the history of continuous service since the modification was made, I see little risk.

stearn-bolt-view-small.jpg
Fig. 6. View of the stern showing position of engine mounting bolt holes and the unusual notch that has been cut into the transom.
stearn-bolt-view-small.jpg (8.18 KiB) Viewed 834 times


The notch is 1-inch deep, and the upper engine mount bolts are 4-inches from the top of the original top and 3-inches from the top of the notch. The exterior portion for the notch has a gel coat surface so I suspect this mod was done long ago.

The modification may have been done 50-years ago or at least prior to the last outboard installation. I assume they wore out a Yamaha 90, the last engine, and the boat was removed from service at that point.

Q1: In the history of this design, what is the mean time between failures of this nature?

Q2: Are transom failures heard of

Q3: Are transom failures never heard of?

Q4: Are transom failures frequent?

The answers to these questions could change my assessment. As it stands I assess the risk of failure due to the notch as extremely low.

Of bigger concern to me are the two through holes below the splash well into the cavity of scooped out foam, that had bolts to attach the last outboard or perhaps a jack plate. I have probed the holes with a needle and one appears well sealed with possible resin, very hard, one hole has a spot where the needle can penetrate say 1/8-inch. I may drill this hole larger, say another 1/4-inch, to assess the inside edges of the hole.

The back side of these two holes expose wood within the cavity where the bolt heads and washers mate with the inside surface. Those surfaces appear solid but I will probe more careful to make sure there is no hidden damage.

This leads me to the [fifth and sixth] question:

Q5: Should I even consider using these engine mounting holes again since they are already there?

Q6: Should I drill them larger then reseal with resin and drill them to fit new mounting bolts?

Q7: Or should I fill the holes and drill new ones above the splash well as described in the how to mount engine to transom posts?

I originally thought to fill the foam cavity and patch the 4-inch access hole. I consider the foam an important part of the structural integrity of the boat and transom. I think patching and filling makes the most sense and to get rid of the lower holes

Q8: Or alternatively, should I repair the lower holes to ensure wood is well sealed with resin, weld tabs on the bolt heads, place the bolts inside the cavity and tie the heads together so they will not turn, pull them tight to the transom, then fill the cavity with closed-cell two-component foam, patch the 40inch hole leaving the mounting bolts as permanent fixtures, and fit a jack plate for outboard mounting?

I really appreciate the feedback and guidance from continuouswave. I have found the operating manuals, performance data for various outboards, engine mounting details, wood locating diagrams etc.

The [REFERENCE long-form illustrated article] "Repairing Hull Damage the Whaler Way" was a great addition to my library--thanks Jim.

I am new to boat repair and restoration, there is lots I don't know and certainly need some guidance. I have a background in engineering and reliability centered maintenance .

rtk
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Re: 1963 16-footer Project

Postby rtk » Wed Oct 09, 2019 2:00 pm

I do not think that I would leave the transom well open in order to access the lower bolts. Way too much risk in that area getting wet even with a good access port hole installed.

It is a tough call on how to mount the engine without raising the transom to the original height.

If you have confidence in the structural integrity of the transom then this what I would likely do.

1) repair the lower mounting holes

2) purchase a CMC ML-65 manual jack plate- https://thmarinesupplies.com/collection ... ack-plates

3) determine how high I want to mount the CMC ML-65 jack plate utilizing the existing two top bolts

4) utilize the top two bolts to attach the top of the CMC ML-65 jack plate to the transom

5) utilize 1/2" diameter by 2.5" length hex head stainless steel lag bolts to attach the bottom part of the jack plate to the transom- two would likely be adequate for a light engine but I would likely go with two on each side for a total of four lag bolts.

I would utilize 3M 5200 adhesive sealant for the lag bolts. I use 3M 5200 adhesive sealant on all engine bolts but many will advise against that due to the perception that the bolts are permanently installed. They will come out with a bit of coaxing.

Now you have a very wide range of engine mounting heights available and you do not have to remove the engine mounting through bolts or lag bolts every time you want to adjust engine height.

I installed an Atlas Micro Jacker hydraulic jack plate on my 1966 16' beginning of the 2018 season. I found one closer to $700. The top of the bracket was bolted to the transom utilizing the standard bolts. The bottom of the bracket was lag bolted using the above referenced method.

https://thmarinesupplies.com/collection ... cro-jacker

When I removed the Atlas Micro Jacker this year to sell the boat the lag bolts were "snug as a bug in the rug" and held up great. The versatility of the hydraulic jack plate was wonderful to have for both low engine height ocean travel and getting into skinny water.

A two piece manual jack plate or a two piece fixed setback bracket is a more economical choice but check with your engine manufacturer on the appropriateness of using a two piece engine bracket. I believe my 60 E-TEC manual or engine mounting instructions explicitly forebode utilizing a two piece accessory engine bracket.

Rich

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Re: 1963 16-footer Project

Postby biggiefl » Wed Oct 09, 2019 2:28 pm

It really depends on time, money and interest. If everything is solid I would stick a jackplate on it and go. If trying to restore then I would fill holes, possibly raise transom up, and drill new holes. If trying to restore to look like new, probably not the correct donor and hence why I would go back to my first suggestion.
On my 24th Whaler. Currently in the stable: 86 18' Outrage, 81 13' Sport(original owner), 87 11' Sport, 69 Squall. :roll:

rtk
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Re: 1963 16-footer Project

Postby rtk » Wed Oct 09, 2019 4:12 pm

Totally agree with biggiefl. The reason I installed a CMC ML-65 on my 16 back in 2006 or so was his extensive use and knowledge of jack plates and set back brackets on 16/17 Boston Whaler hulls. It truly made for ease when playing with engine height, engine swaps and propeller testing. I had a late 1980's 90 Johnson V-4, a 1990's or so Yamaha 115 V-4 two stroke, a 2006 Evinrude E-TEC 90 and a 2014 Evinrude E-TEC 60 on that bracket. Baystar steering/cable steering. The bracket made it quite easy to adjust all these engines to a height that was necessary for the specific application and or performance need.

I have the CMC ML-65 (I think that's what it is but for some reason a 4" setback sounds more familiar) sitting in my garage. I did make the mistake of installing it partially over some old anti fouling bottom paint. Take the dissimilar metals warnings seriously when dealing with aluminum and anti fouling paint contact. Copper based anti fouling and aluminum contact does result in corrosion of aluminum. I don't think the corrosion to the mounting surface of this jack plate is a structural problem for a small outboard. This thing has a max horsepower of 300-400 so I truly feel it will be robust enough for your use.

If you want it I will send it to you just PM me your address. Veterans Day is coming up- when you see the Veteran of War collecting outside your local retail store throw $50 in the box. That's my selling price for the jack plate to you or any other participant here.

Rich

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Re: 1963 16-footer Project

Postby jimh » Wed Oct 09, 2019 4:32 pm

A1, A2, A3 , A4: I don't have any valid statistical data about the frequency of transom failure on a c.1963 Boston Whaler 13-foot boat, and I doubt anyone has any data about any boat. Your question cannot be answered with reliable statistics.

In general, Boston Whaler boats are remarkably resilient and live long and useful lives, and even Boston Whaler boats that have been abused can be restored to decent appearance and good utility. Whether or not the expense and labor of restoration is economical compared to getting a boat in better condition cannot be judged well. Some people like to work on restorations.

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Rick W
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Re: 1963 16-footer Project

Postby Rick W » Thu Oct 10, 2019 7:44 am

Thanks to all. The decision is unanimous: the lower holes get repaired, the cavity filled, and hole patched to as close as original as possible.

cavitysmall.jpg
Fig. 7. Close-up of hole and cavity.
cavitysmall.jpg (18.03 KiB) Viewed 851 times


The notch is 1-inch deep, and the upper engine mount bolts are 4-inches from the top of the original top and 3-inches from the top of the notch. The exterior portion for the notch has a gel coat surface so I suspect this mod was done long ago.

The wood locating diagram shows the 1-1/4 plywood in the transom as 20 x 37. The inside surface where the two "cavity" bolts were mated to looks to be fiberglass.

Q9: Would [Boston Whaler] have wrapped the [embedded] plywood in fiberglass when they made the boat? (See Figure 7.)

I am worried about water ingress from these bolts into the plywood. I would like to drill out the holes and inspect before I patch them.

Q10: How big can I drill out [the engine mounting] holes [in the transom for inspection]?

Was thinking of a temporary dowel plug with a pilot hole drilled through the center. Glue in place and let set, then, using a Forstner bit, drill the hole bigger using the pilot hole in the dowel as the center. I might be able to stop at the inner fiberglass surface. That method should leave a clean hole for the plywood plug.
First time owner, long time admirer , purchased a 16ft hull from Canadian Coast Guard. Boat was actually used and abused by Canadian Fisheries. 1963 vintage (I think) will be sharing the progress and seeking advice

jimh
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Re: 1963 16-footer Project

Postby jimh » Thu Oct 10, 2019 9:44 am

A9: Usually an embedded reinforcement material is placed into the laminate during molding and build-up of the laminate. Wood reinforcements would probably not be wrapped in cloth before being placed into the laminate. Additional layers of cloth may have been applied over the reinforcement in the laminate to improve strength.

I don't know the exact laminate schedule details of a 1963 13-foot hull at the transom. Much of the lay-up in a Boston Whaler is applied with a chopper gun, and cloth would have been used sparingly to add strength in certain areas.

jimh
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Re: 1963 16-footer Project

Postby jimh » Thu Oct 10, 2019 9:45 am

A10: to fill larger holes in the transom a dowel rod should not be used. Cut plugs from similar plywood stock. The transom wood will tend to be in compression, and a plug made from a dowel will have the wood grain oriented differently than the rest of the transom.

Your concern about ingress of water into the interior of the transom and the wood due to leaking at the engine mounting bolts is a proper concern.

One method to insure a water-tight mounting: drill the mounting bolt holes to be slightly larger than necessary. Use epoxy resin to coat the inside of the mounting holes. Then re-drill the holes to the proper, smaller diameter. This method should leave a water-tight epoxy surface throughout the mounting hole. Use proper sealant on the bolts, in any case.

Also, I recommend you use epoxy resin as the adhesive in making repairs. Epoxy is a much stronger adhesive than polyester resin. In making secondary bonds between already cured portions of the original laminate, epoxy resin will make a stronger bond. Polyester resin is mostly used in making the initial primary bonds, when all elements are wet and are in the process of curing.

rtk
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Re: 1963 16-footer Project

Postby rtk » Thu Oct 10, 2019 12:46 pm

For the large hole in the engine well interior side of the boat it looks to be about 4 inches in diameter or so. You have 1 inch of plywood behind the fiberglass skin of the interior shell of the boat.

I would cut say an additional 1 inch of fiberglass off around the hole to expose the plywood beneath. Then I would cut 1/2 inch wide by 1/2 inch deep section of the plywood around the hole. What you will be left with is a plywood hole that is 4 inches by 1/2 inch deep.

This is a method that I have used to fix sheetrock. Use a piece of half inch plywood that is longer than the hole by about 2 inches on each side of the hole but not so wide that it will not fit completely into the hole. Glue the wood to the "back" of the repair. Glue a 4 inch by 1/2 inch plug of plywood to the backing strip. Then glue a 5 inch by 1/2 inch plug of plywood on top of that.

Now you have the plywood portion of the hole filled with plywood and it is flush with the already embedded plywood. The layers of the plywood are stepped to prevent the plug from moving in the smooth 4 inch hole.

Sand the fiberglass around the plug back around two inches to taper/bevel the fiberglass around the now plywood filled hole. Now you can build layers of fiberglass mat and resin over the top of the plug as necessary. Start with a smaller diameter piece of cloth say equal to the 5 inch plywood plug and increase the size by about 1/2 inch or for each additional layer of glass. Build it up to the height needed and you have what I would consider a pretty tight repair that should not require a good deal of filling with fairing compound or the like.

I agree with the epoxy resin for laminating the wood and the fiberglass mat.

For some of the smaller holes in the transom I added some West System 406 Colloidal Silica to the mixed resin to give it some body. Just cleaned the holes a bit and filled them. When you are gluing the plywood a bit of thickened epoxy resin works well to prevent the epoxy from migrating from the repair area and then straight epoxy resin to wet out the cloth. I used the thickened epoxy mix to do as Jim recommends with bolt holes. Straight epoxy/thickened epoxy your choice they will both work. The epoxy thickened a bit stays put a bit better for me.

A fiberglass roller will greatly improve the fiberglass repair. Build successive layers while the resin is uncured. If the resin kicks or gels mix a new batch and keep rolling on the layers. If not you will need to sand between layers. Building successive layers while the resin isn't fully cured will result in an excellent chemical bond instead of a mechanical bond. Save a good bit of sanding also.

http://www.uscomposites.com/fgrollers.html

I would recommend installing the drain tube and doing the repairs in the transom before closing up the engine well. I guess the other decision will be what to use to fill the engine well with if anything at all. I would likely use a product like this to fill the void then close it up for good.

http://www.uscomposites.com/foam.html

Rich

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Rick W
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Re: 1963 16-footer Project

Postby Rick W » Sun Oct 13, 2019 11:35 am

I hate the notch. Yes I have taken a particular disliking for the notch. It screws up the mounting options big time. even for a jack plate. mounting holes are 3 inches down from the notch and 4 inches from the original top. The temple calls for less than two inches from the original top.
I have no experience with fiberglass repair but circumstances are giving me some desire to learn.

The wood locating diagram says the transom wood is roughly 37 x 20-inches.

Q11: Can a section of [the wood reinforcement in the transom] be replaced?

Q12: Can the whole piece [of plywood that reinforces the transom be replaced]?

Q13: Can a dowel [be inserted] in a small piece and fill the gap?

Q14: Given that the mounting holes will be less than an inch from the old notch gap, should a wider piece [of wood reinforcement than the original size] be installed?

Q15: Should the old plywood reinforcement be cut out entirely and replaced?

Q16: Should a fiberglass section along the bottom be left to tie into and the old plywood chipped out?
First time owner, long time admirer , purchased a 16ft hull from Canadian Coast Guard. Boat was actually used and abused by Canadian Fisheries. 1963 vintage (I think) will be sharing the progress and seeking advice

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Re: 1963 16-footer Project

Postby jimh » Sun Oct 13, 2019 1:43 pm

As RTK (Rich) has already described in detail, a good method for installing new segments of plywood reinforcement into the Unibond hull of a Boston Whaler boat is to avoid butt-joints of the wood and instead to use overlapping joints. You should read the information at INSTRUCTIONS--HULL PATCH KIT (that I mentioned in my first reply); that article shows how new materials being added to a Unibond hull in repairs should be feathered and tapered into the original hull materials. The words "INSTRUCTIONS--HULL PATCH KIT" above are hypertext and will take you to the information.

If adding a new section of reinforcement wood at the top, I think making that section wider than the original may add strength to the top of the transom.

If the plywood reinforcement in the transom is in good condition, has not become soft, does not have rot, and appears to be strong, I would not replace the entire piece. I think you have not yet determined the condition of the wood.

rtk
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Re: 1963 16-footer Project

Postby rtk » Wed Oct 16, 2019 7:03 am

If the plywood reinforcement in the transom is in good condition, has not become soft, does not have rot, and appears to be strong, I would not replace the entire piece. I think you have not yet determined the condition of the wood.


Good point by jimh- I was thinking more about the location of the top bolt holes. It's odd that they drilled them so far down from the top of the transom. Makes me wonder a bit about the condition of the plywood between the bolt holes and the top of the transom.

Maybe it would be worthwhile to talk to a local metal fabricator to see how much it would cost to build an aluminum sleeve to cap the gap at the top of the transom. Extend the aluminum down far enough on both sides of the transom, glue it in and then drill new bolt holes in a more standard location.

The original bottom bolt hole location in the splash well can be used but I think you have to move the bolt location "in" toward the center of the transom around 3/4 inches. The distance between the bottom bolt holes in the BIA standard is 9 and 7/8ths of an inch on center according to the template I made.

Rebuilding the transom to raise the notch an inch is a major fiberglass fabrication job. A good familiarity and understanding of the repair process and working with the materials is necessary. Maintaining the structural integrity while replacing the plywood and fiberglass takes a good bit of skill and understanding of the structural build up of materials. Sometimes by taking away large areas of original fiberglass and plywood to fix and area may actually damage the overall integrity of the laminated structure.

Think of a molded fiberglass boat as a motor vehicle that is constructed using the unibody structural technique as opposed to the chassis on frame method. As I understand unibody body repairs typically involve replacing entire sections due to the gross structural nature of the construction method. A bunch of little attachments of light materials equals a strong overall structure. I think I got it a bit right- I am in no way an engineer so I probably butchered the technical aspects of this but that is how I think of a molded fiberglass boat.

Rich