We have a 3.8meter dinghy (Genesis 380 RIB) -- a little shorter than yours. The dinghy itself weighs about 230lbs. The engine
adds another 125lbs. Gas, another 20-40lbs. Anchor
, etc. another 10lbs. Total about 400lbs.
When sailing along the coast, we usually hoist the dinghy (with motor
, gas, etc.) in aft davits that are approximately 8' above deck
level. In addition to the tackle that raises the dinghy, we use a strong ratching strap which keeps the dinghy from swinging.
, we remove the engine
and gas and mount the engine on the stern rail and put the gas in a lazarette that drains overboard
. As the davits are right off the stern, 8' above deck height, I usually don't have a problem with waves. It requires very steep waves to break into the dinghy. Once, in a gulf-stream gale, the breaking waves did splash into the dinghy, but didn't add so much water as to create a problem.
We sometimes store our full trash bags in the dinghy too, although compared to the 400#, that is not a lot of weight.
On my "to do" list is to craft a tent to put over the dinghy so that if I do find myself in steep breaking seas again that any water will simply roll off the sides and not fill the dinghy, increasing its weight and load on the davits. I have seen others who have done this, and they used fenders stored in the dinghy to keep the tent up in the middle.