Measurers Corner

Measurer’s Interpretations and Recommendations

Topic:Hull
Question:Can the floatation system be improved?
ID Number:000012
Date:2008-02-28
Short Answer:Yes 
Answer:This a universal problem is one-design yachts. For the Shields it has been determined that the design of the boat is sound BUT the flotation tanks must be maintained. If they are not checked and kept sound the flotation time after a swamping will be reduced. Sound tanks will keep the boat afloat indefinitely and allow for self-rescue; but open hatches or leaks will give lesser amounts of time before a sinking. It is the Technical Committee's opinion that inspections of the tanks should occur and soundness enforced but no changes to the boat are required. 
Section:§IV-1.7-1.8 
Status:Tabled
Action Date:2010-02-10
Sat Oct 19 11:03:25 2019
DateNameComment
2008-02-28Charles ShoemakerThe executive committee of Fleet 9 has proposed that although there were no swamping or sinking at these two most recent Nationals, we feel insecure about the air flotation, especially with the ruling that allows openings in the rear compartment.
2008-04-03Richard RobbinsThe technical committee discussed this issue (3/12/2008) and agreed that there was merit in the topic. It was decided the committee would work on other issues in the short term and hopefully get back to this issue at a later time.
2008-08-05Charles ShoemakerI believe there have been 5 sinking of Shields out of 260 boats. Two factors that contribute to the failure of the boats to retain their floatation.
1. Failure to keep aft and peak tanks intact. Many of the rubber gaskets are not functional and in talking to Gordon, many of the latches are broken. Also we allowed holes in the after bulkhead.
2. Leaks at the junction of the hull and deck. The integrity of the fore, aft, and side compartments depends upon the deck/hull joint. In many boats portions of this joint have been reinforced, but the junction for the side tanks cannot be accessed and therefore cannot be reinforced.
Some have raised the question about the liability of the class. It is obvious we have known about this for some time, but the problem has not been corrected. If the boat were drier, it might have no urgency. It would be more reassuring that the boat wouldn't sink.
2008-08-05Richard RobbinsMy forward compartment was leaking last season. To fix it I had to remove and re-seat the forward deck wooden handles and bow cleat.
2008-09-09Kurt WeisenfluhHas the possibility of air bags in the forward and rear compartments been considered? Easy to maintain, easy to inspect, adds very little weight obviously. Hard to institute a rule perhaps, but from a common sense standpoint how do you feel about the concept?
2008-10-15John KienerI think as long as airbags do not get in the way of control lines or safety equipment, such as the Anchor and rode, then they should be allowed. There is no performance advantage. It only serves as a good to improve the odds of crew safety, and damage or loss of boats.
2009-08-06Richard RobbinsThe Technical Committee's recommendation is that for the current National Regatta in Chicago the inspection emphasize floatation and the integrity of the bulkheads. The following paragraphs from the Class Rules apply:
SECTION IV - HULL SPECIFICATIONS AND EQUIPMENT REQUIREMENTS
1.7 Perforations - Bulkheads Perforations in the fore and aft bulkheads are permitted. Such perforations shall be made watertight while racing. One or two small holes not to exceed 3/8 inch in diameter may be drilled as close as possible to the top of the aft bulkhead to accommodate lines for trimming the backstay.
1.8 Bulkhead Hatches
While racing, fore and aft bulkhead hatches shall be in place. When in place, fore and aft bulkhead hatches shall be fully seated and secured against gaskets of soft rubber or its equivalent. Hasps of other devices may be replaced or altered to hold hatches in place more securely.
2.8 Backstay Gland
A sheave to turn the backstay pennant is permitted. Sheave must be gasketed to be as watertight as practical.
2009-09-12Richard RobbinsThe suggestion has been made that one solution is to add a pump to the floatation chambers. This makes sense for the aft compartment which does take on water and needs to be sponged out periodically through the hatch. The aft compartment also (in many boats) has the bilge exhaust hose going through the aft compartment which could be T-ed into. The idea would be to mount a diaphragm bulkhead pump inside the compartment with the handle penetrating the bulkhead.

Bulkhead PumpThe class rules would need to be changed to allow for a second pump. The rule is: Section IV-10.1 - Fixed Bilge Pumps A bilge pump permanently mounted to the hull. One through-hull perforation above the waterline or one through-deck perforation is permitted for the exhaust of the pump. One watertight perforation through a bulkhead for the run of the hose is permitted. The location of the pump, the run of the hose and the perforations mentioned herein are optional.
2009-10-21John BurnhamAs someone who's done a good job filling his boat up to the seats on a windy run in Buzzards Bay, I'm curious what attitude the boats that sank took as they went down. Stern first? I'm not wild about the aft pump idea, but if all the boats went down stern first, that might be more interesting to me. Then again, an air bag would probably be cheaper if it were small enough to avoid the backstay purchase.
2009-10-25Gugy IrvingAn account of the sinking of the Shields Black Pearl (#73) on October 10th, 2009 out of TAYC Oxford, MD.

See http://www.shieldsclass.com/measurer/blackpearl.pdf

She was in about 35' depending on the tide which was fortunate as they didn't have time and it wasn't safe to crawl under the deck to get the life jackets. 4 of 5 crew held onto the mast till rescue; the other was on top of some floor boards. She went down stern first in about 1.5 min. Amazingly, she stayed vertical with the keel buried in the mud. Jay is the first to admit he had not gotten around to properly gasket the lines/back stay. Being one of the older boats and a Chris Craft, the tanks were probably not up the newer standards. Jay and I made sure our fleet was aware of the emphasis on floatation.
2009-11-08Kim RobertsVolumes
2009-11-08Richard Robbins
ItemBuoyancy Requirement
Keel43.8 ft3
Other11.9 ft3
Crew14.8 ft3
TOTAL70.5 ft3
2009-11-08Kim RobertsI think that the contributions to buoyancy may be in the order of the following:

Bow 2,519 lbs.
Stern 1,961 lbs.
Subtotal 4,480 lbs.
Seats 1,240 lbs.
Total 5,720 lbs.

This means to me that foam in the bow or stern can't do it completely, but it would help. Also pouring foam into the seat/floor chambers doesn't do it either, but all together maybe. I think the boat weighs under 5,000 lbs. We would be adding 184 lbs. of foam or more.

Pouring foam is difficult, it can over expand and bulge the floor or seats. It can capture water which isn't good, increasing weight, but it also glues the seat surfaces to the hull skin and that is probably stronger and better. It may interfere with repairs. It is expensive and what is not mixed is hazardous waste, and tough to get rid of.

Blue Buoyancy foam is about $125 for 10' so it is not too expensive and almost fits through our access holes which are 24 x 16" ovals. The foam is something like 20" x 8" or 24" x 10". Each Owner could deal with cutting pieces to fit.

The dead wood is supposed to be void, so it contributes to buoyancy and the deck is cored with plywood which could be a little buoyant, and as you pointed out the keel displaces water and contributes to buoyancy, but I think we should just assume no contribution to the problem.
The decks are glassed together with taping on the inside. I bet mine is cracked for 30% of the shear due to collisions suffered. If we fill the bow and stern and sink the boat, the foam could maybe lift the deck off, pealing the taping back, which would be bad as well.

We could test the theories. We could weigh my boat, then we could fill it with foam in the bow and stern defining how one would do it, prove how much it could hold. Then get NEB to launch it with one of their cranes and we could flood it and see how buoyant it really is. Of course, it doesn't simulate the dynamics in a storm but it could teach us something. The foam may cost $750 and crane fees for NEB.

It is hard to simulate filling the seats with foam, because you can't remove it later.

Another thing we could do is make a bolt ring for each access hatches (fwd and aft) to make them really water tight. The bolts would be 5/16" and on 1.5 centers. They could be plywood rings with studs, gaskets and a drill jig. The bulkhead and the cover have to be drilled. Cape Cod could prepare the kits and everyone has to buy them. We could install drain valves. Deck opening would not make it watertight, but it would be better.

I sort of feel that we should do nothing and avoid storms. I then prefer making the hatches to our water tight chambers watertight. Then I would prefer filling the seats with foam, because it is hidden and in the middle of the boat, although difficult, but I admit that it contributes little. Finally I can see putting the foam in the bows.
2009-11-09Richard RobbinsInner liner (one side) for Shields showing the one side tank. The bonding for water tightness is around the edges (near the deck, at the bulkheads and in the bilge. Some boats were never properly sealed under the deck.(Image from Cape Cod Shipbuilding.)
Liner
2009-11-09Richard RobbinsA typical leak area in a Chris-Craft boat. (Image from Cape Cod Shipbuilding)Liner Leak
2009-11-09Richard RobbinsCurrent method for glassing in the liner to bulkhead and bilge. (Image from Cape Cod Shipbuilding).
Liner
2009-11-16Bam MillerI think if we can minimize the amount of water that can get into the tanks, as well as into the boat, we will be ahead of the game. I know the addition of splash boards would help greatly. I also think that each tank should have a method of being inspected by air pressure and soap and water or bubble making solution. It's done all the time on Lasers, to the point where you put a tire stem on a deck plate and pump the hull up. Foam floatation is a nightmare to maintain and will add to the overall weight of the boats.
2009-11-16Andrew BurtonWe should pursue Kim's idea of developing a better way to seal the hatches so they are, in fact, watertight. Once we have a system worked out we could make it available to the members. Though mandating one system is above our pay grade, I think. The hatches could be inspected at the Nationals every year, which would give members an incentive to get them right. We could also ask local measurers to inspect hatches, much as we did with the mast rake measurements.
2009-11-20Bam MillerEtchell's hatch and pump in her forward section. Also notice the inspection hatch.
Hatch
2009-11-20Kristian MartincicFor what it's worth there are other 1d boats that sink. J24's and J22's are both somewhat notorious for swmaping through the companionway hatches and sinking very quickly. Both classes have considered requiring structural changes making them more buoyant after a swamp, but it has always been rejected. The reasons for rejecting that kind of change has always revolved around protecting the 1D nature of the class, and keeping modifications (and the respective costs) to a minimum. I can recall one of my old skippers describing the way a Shields would "sail straight to the bottom (so make sure you get to the vang!)" and it didn't impact my decision to buy one bit.
2009-12-26Andy BurtonBam, the addition of splash rails won't stop sinkings, which are the result of tipping the boat over so far that the water comes in through the big hole in the top (known as the cockpit).
2010-02-12Richard RobbinsMemo from Cape Cod Shipbuilding from 1983.
Flotation test from 1963:Floatation Test - 1963
2010-02-12Richard RobbinsBased on the Technical Committee meeting of 2/10/2010 the following change will forwarded to the Governing Board for its approval:
Section IV 10.1 Bilge pumps permanently mounted to the hull, portable hand pumps, additional buckets and other devices to facilitate self-rescue are permitted. One through-hull perforation above the waterline or one through-deck perforation is permitted for the exhaust of the pumps. Watertight perforations through bulkheads for the run of the hoses are permitted. The location of the pumps, the run of the hoses and the perforations are optional.
2010-05-03Richard RobbinsForward Tank Grounding Corner HoleNotice that the caulking for the grounding strap in corner of the forward bulkhead was bad and there was a clear opening. See picture of “before”. Both corners were re-caulked.
2010-05-03Richard RobbinsBoom Crutch Pocket Found that the pocket for the boom crutch that goes into the aft tank had busted through on one side. This is a clear leak for rain or spray on the deck.