Composite (trudesign) seacocks, for full below waterline refit

[Mitchel Brock]

Hi all,

wondering if anyone has used trudesign composite seacocks throughout their Nicholson?

I’m wanting to replace all seacocks for a uniform system, remove unnecessary, and combine where I can to limit the number of fittings through the hull.

 

thanks,

Brock

 

[Moderator]

On Rainshadow, we used Forespar Marelon seacocks. Being a US-based boat, this made more sense for us. And I didn’t know about the Trudesign option. A comparison of the two seacock construction suggests they are made from similar materials, and meet the same specs. Big difference is the threads for Marelon are US based NPSM, while the TruDesign are BSP.

We started replacing the original Blakes seacocks with Forespar marelon about 17 years ago. Our concern was the Blakes may be going “pink”. In reality, all the Blakes seacocks were in great shape, except the head outline, which had the corrosive impact of holding back black water for the PO. (We put in proper holding tank ASAP).

The Forespar seacocks have provided great service for us. However, there is no way to lube them while in the water, which is a drawback of their design.

One impact of changing from the Blakes is you need to close up the hull thru-holes required for the Blake attachment. So it’s not just a simple replacement.

We used the MF 849 Marelon seacocks with the flanged base. We then made an FRP backing plate with thru holes, and mounted screws so nuts are attached to hold the flange down. This was then epoxied to the hull. The original CN build used plywood backing plates that were gooped down – very easy to get off today.

In this picture, I think we epoxied the screws into position so they will not turn. On other backing plates, we actually used hex head Silicon Bronze bolts, and ground a slot in the backside of the FRP to make room for, and stop rotation of, the bolt head. I cannot find a photo of that.

Despite the Blake’s seacocks being OK, meaning we probably did not need to replace them – I think I feel better about having reinforced plastic through hulls rather than older bronze ones. Certainly its a good idea to rebed thru-hulls if you still have the originals. We’ve found that the goop used in 1974 for Rainshadow’s build is not passing the test of time.

 

Marilyn, moderator

[Mitchel Brock]

Hi Marilyn,

Thanks for sending that through, I’ve found it super helpful! Looks like I’ll take the leap with composite seacocks. I’ll try and document it as best as possible incase anyone is interested, I’ll be altering the raw water intake and copying your maintenance bilge pump setup too…

Thanks,

Brock

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