How to measure a boats length?
 

I'm working on something which is hard to describe. I'll just say there are bits and pieces sticking out over the water which do not help make it float. What are the RULES for measuring the length and width of a boat?

This might come into play when docking fees or insurance are a concern. This topic could also come into play when selling a craft or building to a customer's request.

I'll try to list a few things which could help the debate, if you have a link please post it and save us all a lot of typing.

1. Would you include this bow plank in the boats overall length?
http://www.vysyachts.com/view.aspx?listingid=8
http://www.vysyachts.com/images/8/1506579_27.jpg

2. Would you include this rudder in the boats overall length?
http://www.selway-fisher.com/DoubleEnders.htm
http://www.selway-fisher.com/AmPeapodd1.gif

3. To the tip of this?
http://www.seychelles.net/cruises/english/activities-star-sail-e.htm
http://www.seychelles.net/cruises/im...l--bow-bat.jpg

4. To the end of the sail post?
http://www.crosswindscharters.com/packages.html
http://www.crosswindscharters.com/im...w-lounging.jpg

5. Is this RIB as long as the twin stern tips or the hard hull? How about side to side?
http://www.alibaba.com/catalog/11489199/Rib_Boat_Distributors.html
http://img.alibaba.com/photo/1148919...stributors.jpg

6. I can tell you that hovercraft are often listed with hard structure measuments and when the skirt is inflated (on hover) to help avoid a little confusion.
http://www.atlashovercraft.com/WebPages/Specs.htm

7. You would measure to the bulbous bow (below waterline) of a ship, right?
http://www.menkent.dk/piclexa.html
http://www.menkent.dk/lexapics/sepetiba_lexa_bulb.jpg

cubits?





sorry

Seems to me that if you are going to register a vessel, the registering agency could give you all this information. How about the Coast Guard?

It's just a fantasy design project, don't want to describe or label it incorrectly.

I'm guessing that a snowmobile is not measured from the front tip of it's skis, and a car not from the tip of it's trailer hitch........beyond that I have no sense for this.

Don't know the exact answer to your question. But from my memory (when I used to sail a lot more, back in highschool/college), aren't there 2 measurements that usually show up in a boat's plans? Length overall (LOA) and length at the waterline (LWL)? That somewhat describes the boat, as there are bound to be overhangs at either end. I don't know how marinas/tax assesors/etc. use those figures, though.

Width is usually just given as "beam"--the absolute widest part of the boat, no? I don't think it distinguishes between what's habitable (i.e. cabin) or not (i.e. decking).

Oh, and #4--that big wooden stick is called a bowsprit.

lwl or water line is the shortest but sets the max speed on displacement hulls
loa or overall inc anything sticking out bowsprits rudders ect
lod or deck length is most common messure not inc sticking out stuff

docks charge by the foot of dock space used but rules vary a lot

beam is widest points for fixed hull so outside the airchambers on the blowup boat

draft is what ever it is NOW based on the load carried and when you hit bottom!!!!!!!!

want to get more confused
try to figure messured tonnage
hint it has NOTHING to do with weight or displacement
but is required for government documentation

1. That is the measurement term I was looking for (lod), thank you. It makes the most sense in my situation or contex.

2. Would it be "proper" in the case of the RIB to list "deck length" (LOD) but on the width list the width/beam from the outermost edge of the inflatable? The "twin tails" still rattle me a little on how to handle them.

I would go with the makers numbers
as most of the RIB are ''named'' by the lenght or some varient of it
ie a 100 being ten feet long
others use meters

and as they want to use the longest number I think they do include the tail behind the motor mount

Visuals:

http://www.schrs.com/index.php?page=measurement

As pointed out above there are different measurements for different purposes. The marina you dock the boat at will probably charge you for total overall length. Sometimes the bowspirit or gangplank is not included, just the extension that is structurally part of the boat. Kind of like with buildings the height measurements include spires (which are part of the structural design of the building) but does not include antenas (which are just added onto the structure). Length at water line is probably the most common measurement and the one you'll use to register the boat. Widest width is called the beam.

So if the boat was 50 feet long at the water line and 16 feet wide, you'd call it a 50 foot boat with a 16 foot beam and people would understand what you were talking about. .

My marina measures length overall. In my 40' slip, I have 3' of overhang. That is allowed. They actually come measure the amount I stick out into the fairway. The beam (width) has to be 6 inches less than the width of the slip. Mine, at 14', is 12 inches narrower than the slip.

Google 'Plimsoll Mark' , and you'll get a description of 'displacement tonnage' at various temps and salinities, and how it affects draft. In college, I ran a ferryboat on SanFran Bay. The gross tonnage was 135-ish. The net tons was always 99.7 or something like that. At 100 tons, everything gets big time. My license at the time was 100 tons. I later ran a large yacht, 175 feet, 670 gross tons. 499 net tons. Yes, just under my 500 ton license. Any 'machinery spaces' were deducted from the gross tonnage capability (the idea being that those spaces were not useable for hauling things). I used to illustrate that point by showing guests the closet in my deckhouse quarters. There was no door on the closet. Nestled inside it was the radar computer box, about two square feet of sealed box with cables running in and out of it. It was actually inconvienient (in the radar scheme of things) having it in there. But it made my entire cabin 'machinery space', exempt from net tonnage calculations. That went on all over the ship.

HTH.

Looks like from the link above that LOD (length of deck) is not a standard term for sail boats.

I've been on one wood sail boat from the 1930's (being restored by a lawyer in Detroit back in 1984) which was never raced because of a change in the rules made it to long. The owner did not want to cut off it's beautiful pointy tail to comply.

Thank You to all that have answered my questions.:)

Measurement varies by agency and use - some boat mfg rate the overall length (LOA) to include the bow pulpit - some do not.

When I was in the market for a boat and was doing the boat show circuits I carried a flexible tape measure - 75% of the time, my measurements came in a little different (and less generous) than the mfgs.