3/4" diameter nylon 3 strand twist is fine for your size boat
. 5/8" for small cleats that can't take a 3/4" line, but these should be new and of high quality. Most importantly, have long leads on your lines and lead them upward on pilings if possible. Remember, you are going to see storm surge and your baot might come up 10 feet or more. Maybe a lot more. Once your lines are tight, something gotta give. Best improvement you could make is more cleats, better cleats, bigger cleats, and good backing for them. I have seen an awful lot of undersize or poorly attached cleats bend, break, or most often, simply pull right off the deck
A lot of boats suffer damage from floating up on top of a pier and being stuck there when the tide finally goes out. But even more damage from the boat, securely moored, is pulled underwater.
A cleat ripped off the deck can leave a pretty big hole. 12" of hurricane driven rain has a way of finding such holes. Cockpit
scuppers clog, and water
overflows through all manner of non-openings never before submerged and put to the watertight test. Be sure your batteries
are well charged, and capable of keeping your multiple redundant pumps going for the several days you may be kept away from the boat.
Put out lots of fenders. Put out your dinghy
. Better to lose the dink than get a 5 foot hole bashed in your boat from another boat that has gone adrift.
Remember, your pier will probably be submerged in a full on, dangerous semicircle strike from a major hurricane. Loose boats will cheerfully sail right over your protective finger pier and pile all over you. Any junk rope
you can string from piling top to piling top will help to maybe establish a barrier.
Choice of harbor is important. Our municipal harbor, the outer harbor, sustained probably 90% losses in Katrina. The inner harbor, Orleans Marina, probably lost
10% of boats. Directly adjoining properties, but additional land mass and tall boathouses between the marina and the lake kept wave action down and provided a bit of wind
protection. These losses in the inner harbor were mostly from the very high storm tide rather than direct wind damage. Practically all sails
on roller furlers were of course destroyed, and anybody foolish enough to leave a dodger
it. My own boat is a Katrina survivor under the previous owner, with no major damage except to the engine
which was partly submerged for a couple of weeks and not ran for a couple of years after.
1.5" diameter would be more suitable for a 100 ton trawler
than your boat. I agree, that is overkill. Smaller lines will have more stretch in them. 1.5" lines will require a much bigger cleat than is usually found on a sailboat.
Finally, use figure eights and round turns. Don't half hitch! Your lines will pull tight from underneath and lock themselves down to the cleat! Will require the "rope wrench" to clear them. (pocketknife.) Sure, no big loss, a couple hundred bucks worth of rope
, right? The problem is, during the storm, a good samaritan liveaboard
neighbor braving the storm by staying aboard might slack your lines for you if needed, maybe. But not if he can't untie them. I NEVER EVER half hitch a mooring line under any circumstances. I would get fired immediately for doing something so idiotic on a ship, so I won't do it on my boat. If water is expected over a dock
cleat, I secure the bitter end to the standing part with a piece of duct tape, to prevent the very very rare instance of sloshing moving water somehow undoing all my figure eights and round turns. You DO NOT need to half hitch a mooring line on a cleat and you SHOULD NEVER do so.
Lastly, it doesn't hurt to drop your anchors. Probably won't help. If you are very unlucky, well, maybe it could.
LASH DOWN all hatches etc. The wind can suck them right off the boat and present a very real risk of filling the boat with rain water.
Don't know what else to tell you. Except the best option for the boat is to not have it in the area where the hurricane will make landfall.