Backing plate

[Florida sail]

Would Starboard be an adequate material to use as a backing plate for a stern mounted motor davit? What about the through hull for my new speed/temp transducer? I know that G-10 is the standard, but the cost is significant. All advice appreciated...

 

[Chris Blubaugh]

Could easily be wrong in my opinion, but I would be wary of using starboard in any situation that has a high load...

 

[Ross]

What is the value of the item that you want to mount? Backing plates are insurance.

 

[bria46]

I use starboard for everything, Winch pads, Deck fittings, etc. ... except thru hull fittings. I use Teak or some other wood based material for thru hull fittings. They need to be shaped to the contour of the hull and epoxyed in place.

 

[FastOlson]

Note that almost nothing except 5200 will actuall 'stick' to Starboard.
It makes a good spacer, but for a backing plate you want "fiber reinforced" strength like G10 or epoxy-saturated plywood.
Note that there's nothing magic about the G10 (aka G10/FR4) material. It's just layers of glass cloth compressed with resin.
The further good news is that when you rough up the surface, your new epoxy will really bond to it. That's why it is so nice for projects like thru-hulls, where you seat it against a layer of thickened epoxy. Once you lay a filet around the edge, it's realy a strong and even an attractive installation.

You could make your own at home... speaking only for me (!) I find that it's just as cheap to buy uniform-thickness G10 as it is to lay up my own sheeting.

To reiterate again, with some force you could pull a fastener through a plastic material like Starboard. Rather Unlikely, but possible. It's really not a 'structural' material, per se.

LB

 

[arf145]

I don't believe Starboard is adequate as a backing plate. Like FastOlson and I have purchased FRP for this purpose--got mine from McMaster-Carr.

 

[Dave602]

I have one I made from 3/4" thick AZEC which is a PVC board similar to Starboard. At the top I screwed a piece of Mahogany to the top for the motor to clamp to. I used U bolts to attach to the rail on the stern top and bottom. It works very well with my 4hp Merc 4 cycle. I can post a pic later.

 

[Fred Villiard]

Starboard, almost all of the plastic decking boards, PVC, and the Polys will cold flow under pressure. They will work for thru huls in a pinch, but why take a chance. G-10 FR-4 is not that expensive or you can make your own, Maine Sail has a post on it, do it once and do it right.

Fred Villiard

 

[ironhors42]

Floridasail, since you live in Gulfport. you can go to manufacture of Com Pac which is in St Petersburg, or Largo which is where Catalina builds there and ask both boat builder for some cut or scrap of fiberglass material and use them for backing plates and would not cost you nothing accept time of travel. I sure they be willing to give some away for your project. I have use their scrap for backing plates for my swim ladder and being using them for stanchion later. I hope this help you.

 

[Florida sail]

Thanks to all for your input. What would the appropriate thickness be for a through hull backing plate made form fibreglass or G-10

 

[ironhors42]

The thickness of the backing that I use depend on amount of stress involve on the hardware that on the boat, less stress like swim ladder I use 1/4 inch, more stress like cleat and winches etc I use between 3/8 to 1/2 inch backing of fiberglass including stanchion. I hope that help you again.

 

[RichH]

Starboard is a PLASTIC ... the technical definition of a 'plastic' is that it is a material that will *continually* deform (change shape) when under constant long term high stress (tension or compression) ... called 'plastic deformation' or creep'.

Do not use 'plastics' for 'backing plates' unless the compressive strength of the material is equal to or approaches the values of a 'metal' AND if it does come close to the tensile/compressive strength values of a metal .... the next thing to peruse is its 'creep' of 'plastic deformation' vs. time value.
This includes 'fiberglass' ... it too 'creeps' when under high stress loading for long periods of time.

;-)

 

[Ross]

I rather like durable wood like white oak or black locust for backing plates.

 

[thinwater]

Let's just give the OP a simple answer to his question.

Starboard is just about the least suitable material we can think of, builders don't use it, but DIY's have used it and gotten away with it. DIY's have also used nothing, uncoated ply, and cutting boards; if the loads arn't much and it doesn't leak, it doesn't matter, if they are it fails.

The best solution is probaly solid laminate engineered for the load with a metal plate behind that. Everything else falls in between and may be very suitable depending on the load and the durability required.

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As for G-10, it's strong stuff and you can use MUCH thinner material than Starboard. There are also other grades of FRP. G-10 is generally overkill, unless the application is quite severe.

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In reality, the OP would do fine with fender washers.