Are backing pads necessary for TruDesign seacocks?

[MaxCG]

I'm replacing my seacocks with composite TruDesigns. Are backing pads really necessary when using the load bearing collar pictured? The collar is quite wide and will be bonded to the hull.

Seems to me that by restricting movement it serves the same purpose as a backing pad and I'm reluctant to add extra bulk to what is an already quite large assembly.

My hull is about 10mm thick solid GRP.

 

[geem]

I didn't add them to mine. It is important however, to get the hull you are bonding to, perfectly flat. You don't want the fitting sitting on a high spot

 

[Boathook]

The collar is to support the skin fitting on the threaded part as far as I was aware. A backing pad is to restrict the hull flexing and snaping the skin fitting flange which can happen. This was possibly important with carvel built boats and those GRP that are thin. If you think the hull could flex by the hole it might be a good idea to reinforce with a circular pad with chamfered edges.

 

[MaxCG]

The collar is to support the skin fitting on the threaded part as far as I was aware. A backing pad is to restrict the hull flexing and snaping the skin fitting flange which can happen. This was possibly important with carvel built boats and those GRP that are thin. If you think the hull could flex by the hole it might be a good idea to reinforce with a circular pad with chamfered edges.

You're right that the purpose of the collar is to support the exposed threaded part, but as it provides quite a wide flange which will be bonded to the hull I just wonder if it kills two birds with one stone.

Not sure how much a 10mm hull will flex, possibly a fair amount?

 

[geem]

You're right that the purpose of the collar is to support the exposed threaded part, but as it provides quite a wide flange which will be bonded to the hull I just wonder if it kills two birds with one stone.

Not sure how much a 10mm hull will flex, possibly a fair amount?

I doubt it. Those bases are wide. They spread the load well

 

[Boathook]

You're right that the purpose of the collar is to support the exposed threaded part, but as it provides quite a wide flange which will be bonded to the hull I just wonder if it kills two birds with one stone.

Not sure how much a 10mm hull will flex, possibly a fair amount?

If you are bonding the whole lot in place you might not require a backing pad.
How much a 10mm hull will flex only you will able to tell. To many variables such as gelcoat thickness how big the panel section is, how well laid up, etc.