Safe Boat Size and Wave Height

jkaterenchuk

A recent thread about a poor dive trip got me thinking about a few questions that I have always wondered but never had the opportunity to ask. I suspect the answers will not be black and white but I am hoping to get some relatively useful guidelines. I know absolutely nothing about boats and there operation and I suspect there are many others that are in the same boat as I am (pardon the pun). In my diving career I have been on many different sizes and shapes of boats but to date I have just been a tourist and placed all my trust in the captain and crew knowing whats best in all situations.

Here are the questions:

What are the general guidelines for a certain length boat to operate safely in each different expected wave height? ie...one comment indicated that a 29ft boat would not do well in 3-5 ft seas.

Does this guideline change for boats of different design (pontoon, outrigger, long tail...etc)?

Does this guideline change for any other reason such as location (lake versus ocean, Atlantic vs Pacific...etc)?

What are the other safety things that should be taken into consideration when making a personal decision to board a boat at the dock such that I become the primary decision maker versus a tourist on board? Looking for critical safety items here not comfort items. Since I travel extensively I am interest in world wide perspective.

John

rewrites

My knowledge is limited to various requirements of MCA coding required for boat operations here in the UK. However, might be worth shooting a question over to the guys on BOAT DESIGN. Some knowledgable folk there.

Hope it helps.

PH

JCdesign97

Hi John,

I'll take a break from my normal posture of busting your chops for this reply. :) I am nowhere near an expert on boats nor do I have anything close to as much ocean experience as a lot of people here who should chime in, but I've been out on a good variety of vessels in widely varying conditions so it's a subject that interests me, as well. As you already surmised and IMHO its nowhere near straightforward enough to be able to set a simple boat size to wave height guideline - so many other factors come into play.

The type of boat and hull design play a big part right off the bat in how a boat handles rough seas. Hard chines vs. round bottom will roll differently when taking seas on the beam, but those are balanced out with their efficiency under way. Engine weight and position make a boat balanced or stern-heavy, but of course more engine lets you get out of trouble faster - provided of course that maintenance is kept up and you don't have to worry about a break down at the most inopportune time. Here is a link to an intesting read on small boat safety considerations at sea: Small Boat Safety at Sea: Boat Safety at Sea

As far as location, obviously certain places will get what is considered their normal or average set of weather conditions; but it usually comes down to the conditions outside those norms where trouble starts. As most people with a lot of experience can probably attest, wave heights alone are of little value when deciding if a boat is going to have a good day or bad. Waves are a function of 3 things - height (distance from trough to crest), length (distance from crest to crest) and period (time between crests/troughs). The latter 2 variables can create vastly different conditions for a given boat even among wave heights that are the same. In other words driving to the dock and hearing a marine forecast for 2'-4' seas is almost meaningless until you get out there and see what the lengths and period are ... hence some captains not making a final call until they poke their nose out and see how it is. Here is another link that helps visualize how each of the 3 variables affect a boat on a given ocean state: National Geographic: Wave Simulator--Volvo Ocean Race

When it comes down to making that personal decision whether to board or not, I think some of the things mentioned in the first link (safety considerations) coupled with getting an idea whether the captain and crew are the humble, experienced type vs. the cool cowboy are the biggest considerations. Hope some of that is of benefit ...

netmage

Local guidelines....
1-2: Padipro will sign up...
3's: Padipro starts getting fidgety.
4's on Wednesday: Padipro cancels, everyone else goes diving.
5-6's: Captain cancels unless its a short run and has hardcore divers
6+: Captain is already drunk at the dock.

quickean

Not always the case, but in general a boat that is bigger and heavier with a vee or modified-vee hull is better at handling rough seas. It's scary how much variation there is in boat quality and design though. I've come to find that there are a lot of factors besides length that go into a boat's seaworthiness. There's a lot of variation in what people dive off of too - everything from zodiaks to converted oil industry boats.
While every captain may not be great, they have to have a good deal of boating experience to get their license. It's a good idea to find a boat and perhaps more importantly a captain that you like and trust. A boat that would be seaworthy with one captain and crew may not be with another.
I've found David Pascoe's articles on Yacht Survey Online: David Pascoe, Marine Surveyor and his book "Buyer's Guide to Outboard Boats" very helpful.

mempilot

Oh crap. You are going to be on his list for this one!

mempilot

I hope this doesn't jinx the deal, but I'm buying this to ensure getting Padipro out in seas bigger than 1 to 2 footers:

Attached Images

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Peter Piemonte

Eric: Nice boat.... I'll be looking for a ride to some nice dive sites next time I am in FL.

I ended up going cave diving last weekend. Nice to have the opportunity to do that for a change. Regards, Peter

jkaterenchuk

When can I come down and dive with you buddy?

Can I sleep onboard instead of a hotel?

Your Movie Meg friend for life....John

mountain diver

My boat of choice,