Have one person hold the screw head with a screw driver to keep it from spinning then go below and install the nut and washer and tighten it down..


I will leave you with some general rules for bedding deck hardware:


#1 SEALANT ON DECK - Never bed or use sealant on the inside of the deck. If it leaks you WANT to know about it. By sealing the backing plate side or the inside of the boat you will force the water into the core, if not sealed. You can also cause any trapped water to become starved of oxygen. This can lead to pitting or crevice corrosion of the stainless bolts potentially leading to a catastrophic bolt failure. Only seal the deck side.


#2 TIGHTEN ONCE (tube type caulks) - If you use tube type sealant please don't listen to that old wives tale about letting sealant cure and then tightening it a second time. The second step in that process is waiting for the sealant to change consistency. With butyl, or a marine sealant, done with countersinking, there is no need to wait for a change in consistency. While in "theory" this sounds all warm and fuzzy, and can work if done well, the raw reality is this is often a disaster waiting to happen because it's rarely done well.. With butyl tape you can tighten in until it stops oozing, then you are done. This may take multiple small tightening events for the butyl to displace but there is no worry about it becoming hard...


With butyl countersink the deck hole and tighten it until it stops oozing. Be patient and don't try this in one step. With tube types there are just too many variables that can change the outcome with the "two step" method. It has perhaps been the cause of more deck leaks than if you were to use Swiss cheese to bed your fittings and I strongly suspect Swiss cheese might actually work better, if counter sunk. I have had my moisture meter & sounding hammer on lots of DIY and "professionally" done "tighten twice" boats and there is huge correlation to "tighten twice" and wet decks, huge. Of course butyl eliminates most of these issues...


#3 SILICONE USE - Avoid silicone where you can. There are only two situations where silicone should be used and that is for bedding acrylic dead lights or plastic fittings that are damaged by polysulfides or polyurethanes such as Beckson products. Dow 795 or similar should be used for acrylic ports/dead lights. Silicone contamination of gelcoat is very, very real. It is nearly impossible to clean and remove silicone from gelcoat and auto body products intended for metal are not safe generally for gelcoat. To effectively remove silicone from gelcoat requires judicious manual cleaning then wet sanding rinsing the paper frequently to clear it of silicone traces so you don't grind it deeper into the gelcoat. To test if the silicone is gone spray the area with a misting bottle of water. If the water beads it is not clean.


A customer owned a mid eighties Catalina where the previous owner had used silicone to bed the chain plates. Even after re-bedding they leaked every year for four years straight. He had even resorted to tenacious glues like 3M 5200, still it leaked. He finally called me to discuss it and we simply masked off the surrounding areas with 3M film tape and ground and sanded away the silicone contamination. The chain plates have been dry since, lesson learned the silicone must be COMPLETELY removed before any re-bedding. If you think you've cleaned dry silicone with Acetone, De-Bond or any of the other products folks claim have worked guess again. Over many years I have tried every chemical under the sun to remove silicone contamination and the only thing that works is a thorough manual cleaning and sanding. If you want to nearly ensure that the fitting will leak the next time you re-bed then using silicone is a good way to ensure it..


#4 CLEAN, CLEAN, CLEAN - When bedding hardware clean everything. The deck the hardware the bolts the heads of the bolts etc.. Bolts especially still have cutting oils and residue from machining on them so if you want a good seal clean, clean, clean....