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“Limber” is a nautical term for drains in longitudinals or cross members to allow water to flow to the lowest part of a boat. They’re usually thought of as being used along the keel, but they should be used anywhere water is liable to be entrapped.
Most trailered boats design the limbers so bilge water drains aft to the transom to exit through drain plugs. These drains are best equipped with a removable plug or cap connected to the main body. It’s embarrassing, to say the least, to drop a drain plug overboard or lose it in the bilge. Sailboats or similar craft that have the lowest point in the bilge close to the longitudinal midpoint will have drains in the bottom. In either case, bilge pumps that purge the water from the boat can be used; this is a must for boats that remain in the water.
Fresh water allowed to sit for long periods, particularly in a wooden boat, can raise havoc. Boats on dry land stored with or without a cover should have the drain plugs removed. If the drains are at the transom, the tongue of the trailer should be raised so any rain or condensed moisture will drain out.
How many and how big should limbers be? On a fully framed boat where frames contact the bottom, limbers should be cut in the frames on the outside of all longitudinals. Make the limbers as large as practical without weakening the structure. Too small openings can readily be plugged by bilge debris.
Boats that are trailered to and from the water are usually washed down after use. It is imperative to have all water drain aft to exit through the drains. Having to use a sponge to remove water pocketed in areas that won’t drain is tedious and unnecessary.
A common area for water to pocket is alongside the longitudinals, usually battens, as they junction with the transom. A notch cut athwartship on the batten as shown in the photo below enables water to flow to the centerline alongside the keel and out the drains. Such a notch should not cut away more than half the longitudinal and a reinforcing block should be used on the inside over the limber.
Limbers should be cut during the building, usually just before planking the boat. Think ahead and consider how bilge water will flow to the drains. Cutting limbers after the boat is built is both tedious and usually sloppy. Thinking ahead will save a lot of unnecessary hassle.
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One Response to Designer’s Notebook: What Are “Limbers”?
I and a friend built the Power Yak. We altered the design so as to permit the power system to be raised up into a well so now the boat only needs 6 inches of water to float it. With the Minn Kota raised I still have headway and reverse. I use a rudder off the stern for stearage. The boat has a bow light and a removable stern light for evening cruises. The boat also has a raised coming completely around the cockpit.
There is sufficient floatation that hull will not sink with 500 lbs aboard and one deep cycle lead acid battery. The boat can hold two batteries just aft of the rear seat and one in the front by adding a tray there. The boat has been underway in water with 12 inches or more of waves and I had no issues – that is as long as you keep yourself dead centre. Two hours and 15 minutes only ran the one battery down 35%. GPS says the boat does more than 5 mph at full speed with two big guys on board.