Control lines through deck

[RoyB]

This may not strictly speaking be a rigging question but I know someone here can point me in the right direction.

For a 31 foot frac rigged asymmetric inshore race boat I am considering running the new two ended backstay controls under deck and out again near the traveller. The reason is to avoid more stuff underfoot for the helmsperson to trip over in the cockpit.

The only sticking point is that I don't know the best way to seal up the penetrations so that 3/16 spectra double braid can pass through with a minimum of moisture.

The cockpit is always dry except for spray, rainy days and boatwashing. The boat doesn't go offshore so oceangoing seaworthiness isn't mandated. If I do have penetrations in the deck I'll make some quick-install protective covers that are truly waterproof just in case.

I know that nothing I can fabricate will be completely waterproof . I've considered making some tightish leather or rubber seals with rope-sized openings.

Surely there's a correct way to do this?