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Wiley Baggins
12-07-2002, 05:50 PM
I'm interested in the various schools-of-thought and experiences with self-bailing decks on small powerboats. In looking at some of Bolger's writings/comments, he indicates that a self-bailing deck should be on the order of one foot above the "normal waterline." If one desires a self-bailing deck on a relatively small skiff (not to exceed 20 feet in length), this would push the sheerline up quite dramatically to achieve a reasonable gunwale height as viewed from inside the boat (this assumes that one wants to brace themselves with their legs while working at the side or over the transom).

Also, in looking at an old reference to Norwegian requirements for scupper area, the following formulae and information are given.


Area(cm^2) = 40+15 x area of cockpit sole (m^2)

or

Area(sq. in) = 0.155 x (40 1.4(area of cockpit in square feet))

The accompanying calculation for a 2m x 2m (or 6.56 ft. x 6.56 ft.) deck works out to two drains of ~80mm^2 (~3 sq. inches).

from "Designing Small Craft" by John TealeObviously, there is much to be said for the standard practice of placing a couple of drains at the transom, but I am curious if anyone here has done anything with supplemental freeing ports along the boat's sides.

For further clarification, I am talking about boats like the Ocean Pointer and West Pointer; basic small lobster skiffs with center consoles, or similarly sized/shaped bass boats with small cuddies.

So, who has a self-bailing deck and/or thoughts on the same?

On Vacation
12-07-2002, 06:08 PM
Wiley, this is my thought on this one. One foot is a lot and never ever used in even fiberglass boat building. A twenty foot open runabout at most will have around 24 inches inside deck freeboard. Depending on the type bottom, eight inche draft is a average. So if you choose to have a self baling freeboard, then you will have a real mimimum inside to the knees to lean on.

If the boat stays on a trailer, my thought would be to forgo the self bailing and put a bilge pump well in the stern and enjoy a nice height for comfort and safety inside.

Wiley Baggins
12-07-2002, 08:19 PM
Oyster,

Thanks for your thoughts. One foot does seem like a lot, but it does not seem unreasonable to me, beyond the challenge of keeping the proportions of a hull within reason. I am hesitant to draw too much from comparable fiberglass boats, as many of them use cored construction which provides supplemental flotation.

At this juncture, I prefer to consider scuppers/freeing ports since there is no pump to fail. As you indicate though, meeting the one-foot "rule" is a challenge. Using your numbers, a twenty-foot open boat would have a minimum keel-to-gunwale measurement of 44-inches, and 36-inches of freeboard. When you add in the additional height at the bow, a simple skiff begins to be quite bulky, and take on quite a bit of weight and windage.

On Vacation
12-07-2002, 08:32 PM
Here is an example of a 20 foot center console runabout. NOtice the fellow standing a the center console and where his knee joint are located. If the boat is self bailing the inside deck is no more that about 14 inches in the stern.

You can choose to do one of two things. If you choose to have a low profile boat, you will be unable to have a self bailing deck and enough inside freeboard to safely lean against without your center of gravity being transfered to the higher region of your body.

The only alternative is to install a raised caoming inside the covering board.
http://www.boatdesigns.com/cgi-bin/store/web_store.cgi?page=sportman20-18.html&&cart_id=1908977_18218

Wiley Baggins
12-07-2002, 09:26 PM
Originally posted by Oyster:

... If you choose to have a low profile boat, you will be unable to have a self bailing deck and enough inside freeboard to safely lean against without your center of gravity being transfered to the higher region of your body...
That about sums it up. The questions now are...

1. Who has built/used a boat with a deck like this that has adequate gunwale height?

and...

2. What are their impressions of this arrangement in service?

On Vacation
12-07-2002, 09:42 PM
In an average 20 foot wooden boat or cold moulded boat, you can obtain a marginal self bailing hull with 27 inches inside of freeboard, 8 feet wide, with 10 inches of draft. The bow will end up a minimum of 39 inches from rail to waterline.

gary porter
02-06-2003, 01:22 PM
Here is an alternative that doesn't quite fit some of the above criteria.
I posted some of this in the chine flats post but here is a bit more info.
Not sure if technically these are scuppers but thats what we call them.
The sides of the boat are approx. 29" 30" at the transom and the inside
freeboard is probably 3" less. You can see in the photo below , the
deck is at the botom of the pipe. This is a section of fiberglass drill tube
epoxied in to the transom. On that is placed what amounts to pump hose
but I have mine made up as blue was the only color I could by premade.
As you can see by the other photo when sitting in the harbor , fishing etc.
we pull up the scuppers and drop them under way. If I forget as I do
sometimes a slight bit of water will seep in but not much. When loaded
the scuppers will ride at or slightly below the waterline, the boat doesn't
draw much water. When under way any water drains quickly. They also
work well for allowing water to drain when on the trailer. I have a sump
pump but haven't found a use for it yet.

http://www.imagestation.com/picture/sraid50/p17530e78c46309c14d16d1826a27397b/fcacfbf1.jpg
http://www.imagestation.com/picture/sraid50/p93c49aa49edeedac58c71ce5e8bf9632/fcacfbef.jpg

The boat is a Tolman widebody 21' 6" x 7' 6" Renn Tolman , the designer is who came
up with the scupper design,,,,I think. Anyway he and many others use the same design and I've heard no complaints. I would like to see what others are doing as well.
Gary

shadow99
02-07-2003, 03:32 PM
I use this style of self-bailing rig. A piece of 3/8" Brass or copper tubing, create a loop so that the top of the loop is above the waterline. One end stays in the lowest section of your bilge, the other end passes outside thru the hull, with the end of the tubing facing aft (in front of the prop works best). As long as the boat is moving forward greater than 3 knots, the low pressure created below the boat outside will continuously suck out the water in the bilge. I use this trick on my RC powered fleet, and I found out that it works great on my 15' sailboat as well. No electrics, no moving parts, no worries.

Rick

Alan D. Hyde
02-07-2003, 03:43 PM
If the bulwarks are too low with the deck raised as you describe, railings around the cockpit would add less windage (and perhaps do less damage to the boat's looks) than would building the bulwarks higher (raising the gunnels).

Alan

dcobbett
02-09-2003, 08:34 AM
Regarding the discussion of scuppers and self bailing decks and the comments attributed to Bolger that I saw on the Chin Flats thread, isnít the issue one of inappropriate distribution of floatation, possibly in conjunction with inadequate buoyancy, rather that the desirability of self bailing decks and scuppers? By itself, a self bailing deck may enclose sufficient volume to provide the desired amount of buoyancy, but not necessarily in locations that insure a hull stays upright in a swamped condition (the Bolger example).

It seems to me that if you have a self bailing deck with scuppers and get pooped, open scuppers will flood and add to your problem unless the volume of floatation between the LWL and the underside of the self bailing deck is at least slightly more than what is required to displace the weight of water inside the hull. With outboards, another factor would seem to be the transom cut-out. Wouldnít you need enough floatation/bouancy inside the hull to insure that the water inside the hull started to flow out through the transom cut-out before the hull sank to the point where the actual LWL was at that same level?

I donít have any professional credentials relative to this issue, and I donít think Bolger needs to be defended, but he might just be saying that to meet these criteria, his experience says the average 18 to 20 foot open skiff would need a cockpit sole that is about a foot higher that the LWL and this has, in his opinion, undesirable consequences.

Wiley Baggins
02-09-2003, 11:52 AM
Gary-That is a very interesting technique. It looks like summer in the photos. Are you guys dressed for boating, or is it colder than it looks?

shadow99-The siphon tube is a good way to go when you have headway, but Iím hoping to solve the problem with non-dynamic bailing. It may prove to be unrealistic goal.

Alan-Nice, practical approach, but my sense of aesthetics (limited, Iíll grant you) would prefer the bulwarks to the railings. The windage issue is a serious one, and may be the deal-breaker.

dcobbett-You make some great points regarding to the aggregate effect of freeboard (as measured from the deck), scupper area, and buoyancy distribution, and I am sure that played a factor in the example given by Bolger.

In the boats that he uses as examples of a better approach, one (the Diablo Grande) has a self-bailing deck, and the other (the Plain 18 Skiff), does not. In the case of the Diablo Grande, the boat has a full-length, weather-tight deck, very little in the way of bulwarks, and a series of shallow foot-wells. The Plain 18 has no scuppers, and a significant amount of flotation, and more conventional measurements from the deck to the gunwale. Both boats have slop wells for the outboard that are separated from the cockpit by a bulkhead.