Transom Repair

This is my first transom repair, so I'm hoping to get some advice. I started this by cutting the stern on each side of the storage compartment, drilling out the rivits and removing the top section. I then cut out the inner transom wall and removed the rotton wood. There was a middle sheet of fiberglass, so I cut it out and removed the wood on the other side. After a couple of days, spread over a few weekends and some homemade tools, I removed all of the rotton wood completely from the transom. I am considering reattaching the back piece of fiberglass and cutting two pieces of plywood to fill in the gaps and then using a epoxy filler to fill in any spaces. I have reading articles from, The Rot Doctor and Seacast. After reading some post on seacast, I'm not to sure about using that. The transom will support a 30hp Johnson. Any advice would be a great help.

 

Build it like the original and it will last you another 25 years. Cut two layers of 3/4" plywood. Exterior AC works fine. Put a layer of 3/4oz mat on the transom soaked in polyester resin and set the first layer of plywood on it. You need to screw and or clamp it tight. Let it set overnight and then put a layer of mat soaked in polyester and screw the second layer of plywood with 1 1/4" galvanized drywall screws. Put about three layers of 4" wide mat on the edges and two layers over the rest. Drill and install a new drain and you are done. Epoxy works fine, but it is goldbricking,

 

have you thought about Seacast? I was reading some of the older posts and there was some give and take about getting info out of them.
Well things have changed since then. Seacast is now supported by a full crew ready to help everyone that calls. They spent lots of time with me and helped review the pictures I sent. After years of only wood boats florida is fiberglass boat land. There is now info on the web site and so far the stuff seems to meet everything they told me. poured the transom and going for the stringers next. I was worried when I saw all the old posts but they seem to have new management by the daughter of Mr. Unger. Check it out

 

You are accurate in your post about SeaCast. Is an incredible product that is much lighter, & stronger than wood core transoms. A 1.5" transom poured with SeaCast, compared to an identical dimension transom formed with 2 plys of 3/4' plywood/resin/mat has almost twice the load carrying capacity of the wood core transom. The SeaCast poured transom has over double the impact resistance of the wood core transom, as well.

The best description of SeaCast is a pourable composite matrix (resin, fillers, binders, activators, and recycled fiberglass fibers) that is impervious to water when cured, sticks to older fiberglass / wood based products found in the bottom of the transoms and side gunnels, can be molded, shaped, drilled, tapped, & sanded.

I am confident in what I am sharing, as my company is the Georgia distributor for SeaCast. Don't mean to hijack the thread, just wanted to chime in on the prior comment.

 

What is the weight of 1 Square Foot x 1-1/2" thickness of SeaCast?

 

To answer your question, 1 each 5 gallon pail of SeaCast contains 1,000 cubic inches of finished product (SeaCast Matrix, fiberglass, and tubes of BPO catalyst). The shipping weight of a 5 gallon pail totals 33 pounds (includes plastic 5 gallon pail, shipping box, labels, and plastic tubes of BPO catalyst). The net weight of finished product is approximately 31 pounds. A 12" X 12" X 1.5" section of finished product requires 216 cubic inches of finished product.

31 pounds of finished product divided by 1,000 cubic inches yields .031 pounds per cubic inch X 216 cubic inches in the 12" X 12" X 1.5" section for a total of 6.70 pounds.

Hope this answers your question.

 

Thank you ninetogo.

I reviewed the instruction manual at http://www.transomrepair.net/images/manual/SeacastManual_July_2011_WEB.pdf and was perplexed by page 16 which says:

It doesn't specify what area that figure is for.

I appreciate the information you have provided here.

It would also be useful if someone compared cost, weight, and strength of seacast to not only traditional marine plywood but also the composite boards:
http://www.boatdesign.net/forums/fi...g/non-wood-transom-wood-substitute-39286.html

 

I think what the author was attempted to share by that statement, is that SeaCast is roughly 1/3 pound lighter per square foot (12' X 12" X 3/4") when compared to marine grade plywood (12" X 12" X 3/4"). As most US built boats (bow riders, bass, center console with lengths from 16' to 26') have a 1.5" core thickness for the transom with 1/4" inner and 1/4" outer fiberglass skins for a total of 2" of transom thickness.

This statement is attempting to share that SeaCast, when poured to a 1.5" thickness inside a transom, will weigh 2/3 of a pound (10.6 ounces)less per square foot of transom surface area as compared to marine grade plywood. The truth is that SeaCast is actually lighter than the 10.6 ounce representation due to the fiberglass cloth / resin used with plywood construction to bond the plywood to the outer fiberglass skin, additional resin-fiberglass mat used to bond the 2 plywood layers to each other and finally the resin-fiberglass mat used to encapusulate the exposed plywood surface on the inside face of the new transom.

Per my previous post, SeaCast weighs approximately 6.7 pounds for a section measuring 12" X 12" X 1.5". A section of Plywood (12" X 12" X 3/4" X 2 pieces stacked to equal 1.5" thick)with 2 plys of 2 ounce mat + iso-polyester resin (X 2) will weigh approximately 9.6 pounds. You can do the math to calculate the total square footage of the transom surface area and multiply X 2.9 pounds differential per square foot to see the weight difference.

 

I have a old Zodiac thats 3.3 meters long and still has no holes but has a rotten transom its rotten right across the bottom so much so it has been replaced. everyone says it cant be fixed for a reasonable price would Seacast be for a blowup or not? and at what cost? also can it even be found in Australia? Thanks

 

Seacast™

Yes you can get Seacast™ in Australia there is a distributor there. Here is the contact info. I am sure that you will be pleased with the results. I know of many boats done with Seacast™ and the only complaint came from one yard that just slapped it on like it was mud and did not follow the directions at all. Every properly done Seacast™ repair has left people pleased with the results.

THIRD QUARTER PRODUCTS & SERVICES
3 Delgaun Place, Baulkham Hills
NSW 2153. Australia.
Ph: +61 (0)412 127 348
Email: thirdquarter@bigpond.com
Contact: Steve King, Director

 

So let me understand this now, if a 1.5" thick, 12" square of Seacast weighs 6.7 pounds, then comparing apples to apples; a .75" thick square of the same dimensions is 3.35 pounds. 32 square feet (number of square feet in one sheet of plywood) times 3.35 is 107.2 pounds. So, The 64 pound sheets of 3/4" Douglas fir plywood I'm buying must be some kind of miracle wood in comparison to what you must think plywood weighs? Honestly, I use Meranti as often as I do the fir, which weighs in at 72 pounds per sheet, so how's Seacast lighter again? It must be that modern math thing again.

 

Seacast weight 31 lb per 1000 cubic inches

don't forget the glass and resin when you add the weight. Seacast is 31lb for 1000cubic inches which equals 1.5 lb per sqft x 1.5 (for the transom thickness) equals 72.5 lb for a 4 x 8. I don't know where the 6.7lb number came from. but when shipped the Seacast 5 gal kit with pail, box, and packing foam is 31 lb and is 1000 cubic inches. So your wonder plywood isn't such a wonder now is it? thanks for keeping the thread going it givess me something to do these fall nights in florida. check my math I may have made a mistake not perfect yet.