Strengthening gunwales for wakeboard tower installation

[rengnath]

Hi everyone,

I?m a new poster to iboats but have read several threads here before. I am looking for advice on how to strengthen the gunwales on my boat to install a new wakeboard tower.

The boat: 2011 Bayliner 185 bowrider, 3.0 Mercruiser I/O Alpha I gen II
The tower: Aerial Ascent 2.0 ? 2.25? diameter tubing, 4-single bolt mount points, will be doing a ?side-mount? installation

I was planning on using 3/8? plywood to strengthen the gunwales. I don?t have the boat home until spring so I am not sure on exactly how large the planks will be, but I will fabricate them to be as large as possible. I am looking for specific advice on how to bond the plywood to the existing gunwale. Important note: I have NO experience working with fiberglass.
I have reviewed the following options:

1. Mixing up a batch of Oops or Friscoboater?s peanut butter and coating between the gunwale and the plywood to make a structural bond of the fiberglass and wood
2. Using 5200 or marine epoxy
3. Purchasing premixed Everglass Short Strand Reinforced fiberglass filler or Bondo Long Hair Filler, both are about $15/quart from Amazon

I need help on picking one. I know option 1 would be the strongest, however it will be the toughest option for a beginner and the most expensive. I?m not quite sure how much I would need or the best place to order the supplies from.
Option 2, 5200 is permanent, readily available and has a nice amount of workable time. This is what the reinforcement kit from Aerial comes with. I?m curious as to how well it will make the hull and plywood bond for structural strength, as this is what Aerial recommends.I have seen a couple installation threads on here that use the same method.
Option 3 is the one I have the most questions about. It seems to be an easier alternative to option 1, however I?m not sure if it will give me the strength.
Thanks for any feedback.

 

[sphelps]

Will it be a through bolt assembly ? I would do the poly or epoxy resin PB .. Put a layer of csm on both sides of the plywood before gluing it in if your using poly resin . Epoxy pb just pre coat the wood with the resin then glue in .. Will it be seen or hidden under the edge of the gunwale? 5200 on a vertical surface gets a little runny ...

 

[rengnath]

Thanks for your response, sphelps.

I've been pricing out West System and MAS supplies for peanut butter. I can get 1.5 gallons of MAS (resin with harder) plus the silica for under $200. I was thinking approximately a quart per mounting point, but I definitely don't want to run out.

They are through bolts. The instructions call for a 27/64" drill bit and the through bolts will be an M12. They supply an aluminum backing plate, but it's more of a fender washer.

The gunwales are completely hidden, which will be hard to work in but it doesn't have to be pretty, just structurally strong.

Will I want to do a layer of CSM over the piece of plywood and on to the boat gunwale, or just cover the piece of plywood?

 

[Woodonglass]

You don't use CSM with Epoxy, just use some 8oz fabric.

 

[rengnath]

Thank you! I missed in my research that you don't use CSM with epoxy resin.

So I will put 8 oz on each side of the plywood. Do I also want to do a layer of 8 oz on the boat before I peanut butter the plywood on? And will a final layer of 8 oz over the plywood once its peanut buttered to the gunwale increase strength, or will it just be overkill? I would wait for each layer to cure before moving to the next step.

 

[sphelps]

How big are the pieces of plywood going to be ? Seems like 2 qt is a lot for just a couple spots . idk .. Ihave never used epoxy but I would think just bevel the edges of the plywood at a nice angle .. Coat it with the epoxy resin paying close attention to the edges .. let cure then with the thickened epoxy, pb butter up the inside of the gumwale and the one side of your plywood . Install clamping it together somehow . Smooth out any ooze around the edges , let cure , sand the bumps off if needed . Then lay the layer of 8 oz cloth lapping over onto the gunwales a few inches and your done .. Might use some 5200 on your through bolts to keep any water from seeping in ..
Btw, don't clamp the piece in too tight other wise you'l squeeze out all the pb . Just snug it up ..

 

[Scott Danforth]

Does an 18' boat with a 3.0 have enough power to pull a wake board skiier? My first thought is you may need a bigger boat and motor to go along with the tower

 

[jigngrub]

Does an 18' boat with a 3.0 have enough power to pull a wake board skiier? My first thought is you may need a bigger boat and motor to go along with the tower

Nah, they just plow through the water at lower speeds wreaking havoc on docked boats and unprotected shoreline.

 

[rengnath]

How big are the pieces of plywood going to be ? Seems like 2 qt is a lot for just a couple spots . idk .. Ihave never used epoxy but I would think just bevel the edges of the plywood at a nice angle .. Coat it with the epoxy resin paying close attention to the edges .. let cure then with the thickened epoxy, pb butter up the inside of the gumwale and the one side of your plywood . Install clamping it together somehow . Smooth out any ooze around the edges , let cure , sand the bumps off if needed . Then lay the layer of 8 oz cloth lapping over onto the gunwales a few inches and your done .. Might use some 5200 on your through bolts to keep any water from seeping in ..
Btw, don't clamp the piece in too tight other wise you'l squeeze out all the pb . Just snug it up ..

Thanks sphelps, that's what I needed. The pieces will be about 5x8" give or take an inch depending on what the gunwale will allow for.

Does an 18' boat with a 3.0 have enough power to pull a wake board skiier? My first thought is you may need a bigger boat and motor to go along with the tower

I didn't think so until one of my 200lb friends got behind it this past summer and did it from the ski hook with 4 people inside the boat and a 19" pitch 4 blade prop. He's an intermediate wakeboarder, by no means an expert. That being said, while we will wakeboard from the boat, the tower is being installed for some other functionality as well. I needed a spot to securely mount 6 rod holders for trolling for salmon, and in addition I will now have a bimini.

A bigger boat would be nice, but I'm only 24 and I have something that gets the job done for now.

 

[Quick3201]

Just be sure all surfaces you want to bond are sanded, clean, and dry. Good luck.

 

[sphelps]

Just be sure all surfaces you want to bond are sanded, clean, and dry. Good luck.

Yep an acetone wipe down before you start glassing .. I would think you could use poly resin ... It would be a lot cheaper . Make sure you cover up everything under the area . It' gunna be a little messy ... Post some pics of what your doing ! We love pics no matter how big or little the project !

 

[ondarvr]

There are a couple ways top go about it.

Use 1/2 ply if possible, or even thicker, the surface may not be flat where it needs to be though, so filing may be needed.

Drill a hole or two for the mounts prior to doing anything else so you can see how thick it is, thicker is better. Sometimes if it's thin you need to build up a larger area or it will flex and crack. Thick glass may need no support other than the plywood backer, it can be as easy as using 5200 or some store bought epoxy putty to bond the plywood in place. But in reality the through bolts are doing all the work, the glue or putty are just making sure the plywood is in complete contact with the glass.

Typically these locations stay dry, so rotting wood isn't that big of a concern.

The other option is to glass them in completely, this includes glassing an area larger than the wood prior to putting the wood in place and glassing over it. If there's room and the person does glass work, it's easy, for a first timer it can be a mess.