As the 2nd week of Jan ends, here at Bowdidge Marine Designs this year is shaping up to be BIG. Every day whilst working on new designs, answering emails or phone calls, our large printing plotter is working 7 days a week, printing out plans bound for all 4 corners of the globe.
In regards to new designs, I must get on average 2-3 calls per day, asking about a new design, let alone emails. So overall, its great to see Bowdidge Marine Designs marking its mark around the world.
As for our boat building forum, it great to see so many members sharing their builds at various stages of construction and also launchings. Some members are now into their 2nd and 3rd builds, slowing stepping up in size with their boats.
For example, Geoff who is now into his 3rd build (a Tropic 14, a Magnum 12 for his father and now a
Sea Strike 16, made up a small video about how unsinkable his Tropic 14:
Click HERE to view
On another note, we regularly have articles about our new designs in the Australain Boat Mag, a great Australian boat mag about anything to do with fishing/ boating and anything else for that matter.
Peter (the editor) writes:
Enjoy - and dont hesitate to flick the link on to your friends and colleagues, as we are taking a much more aggressive circulation stance in 2014, as we grow Australian Boat Mag back up into the 8,500-10,000 openings (circulation) asap. So the more people who get to see and appreciate this issue the better.
To see more of this great ozzie boating mag, click the link below:
ABM Issue #206 January
http://theboatmag.boatmags.com.au/?iid=86067
All to often we often hear of people leaving port, driving off only to realize that theyve left their bungs out and their boat is sinking. With inadequate buoyancy foam and bilge pumps, they turn around and make a mad dash for shore, often beaching their boats either at the beach of at the ramp in order to save their boat from sinking.
As we all know, bilge pumps would have to be on the top of the list for any boat. Failure to do so can result in water damage, loss of stability, and even sinking. Even so, water will find its way aboard through drips in windows, through hatches and ventilators, and through spray or rain entering an opening.
In rough weather, solid water will come on deck, finding its way below through everything from chain pipes, hatch gutters or to a door left open for to long.. Then of course there are leaks in the hull itself. These could be small drips through packing glands, damaged fittings, or- the worst fear- a sizable hole from a major impact.
As well see even a seemingly quite small hole below the waterline can admit a substantial amount of water very quickly.
REQUIRED BILGE PUMP CAPACITY:
There arent many regulations for pleasure craft pump capacity. We can refer to the ISO 15083-2003 (categories A,B and C recreational boats) and AS1799 standard for some guidance.
GPM - gallons per minute
LPM = litres per minute
ISO boats less than 19.6ft (6m): = 2.6 GPM ( 10 LPM or 600 litre per hour)
AS1799 boats less than 33 ft (10m): = 17.44 GPH (66 LPM or 3960 litres per hour)
As you can see, there is quite a variation in minimum bilge pump capacity requirements.
ESTIMATING FLOODING RATE FROM HULL DAMAGE:
The minimum recommendations for bilge pump capacity seems too low. We can check the minimum required pump capacity against the approximate flooding rate from a rather small hole in the hull below the waterline. The following is a reasonable approx formula for flooding rate:
GPM = 5.56 x d^2 x ((sq.rt)H)
d = approx opening diameter, in
H = depth of opening below the waterline (head), in
Example:
Lets assume a simple puncture of approx 2" (50mm) diameter located 6 in (152 mm) below the waterline for a power boat or yacht.
5.56 x 2 inches^2 x ((sq.rt)6 inches) = 54.46 GPM
5.56 x 4 x 2.449 = 54.46 GPM
Whats interesting is: 54.46 GPM x 3.785 = 206.13 LPM !!!!!
If you were unlucky enough to get an impact 1.5 ft down ( 457mm) with the same hole diameter, then the amount of water pouring in would be approx 94 gallons per minute or 351 litres per minute !
Whoops - unless you have some form of foam flotation or sealed air compartments, your going down, unless your boat is made from wood. Even still, you would still want to have the capacity to pump the boat out faster than the water is coming in !
You can quickly see however, that even a hole of modest size (and not all that deep) will quickly exceed the minimum bilge pump capacity required above. There are practical limits to how large a bilge system you can and should install, but I recommend more than the minimum requirements given by the standards above.
SIZING UP A BILGE PUMP FOR THE REAL WORLD:
Many manufacturers bilge pump capacity ratings arent all they ought to be. Most manufacturers rate their pump capacity with no hoses attached and with no lift (head). Those that do rate for head state this clearly, and its usually a nominal 10-ft of 3-metre head or height. However, not a boat in existence operates a bilge pump with no lift or hoses attached.! Also, the friction in 3 to 6 feet (1 -2 metres) or more of hose and pipe commonly found in all bilge systems cuts the flow rate, and the batteries are seldom delivering full oomph.
Manufacturers rate capacity in gph (gallons per hour) or gpm (gallons per minute); or in metric lph (litres per hour) or lpm (litres per minute) Unfortunatly, that shiny new pump rated at, say, 1,500 gph (5,700 lph) in the catalog will seldom deliver more than half that in a real- sevice installation. Indeed, 40 percent of rated capacity is about the norm. In other words, the real flow out the thru-hull outlet from this 1,500-gph (5,700 lph) pump will be about 600 gph (2,280 lph)
Allowing for this loss in flow rate, whats the minimum pump capacity that should be installed? The following will give sensible results.
Pump Capacity (gph) = 1000 + (100 x displacement in long tons)
Or
Pump Capacity (lph) = 3,785 + (372 x displacement in metric tons)
Example:
Assuming a boat has a displacement of 2200 lbs (998 kg or .998 metric tons)
Long Ton = 2240 lbs
2200 lbs / 2240 = .982 long tons
1000 + (100 x .982) = 1098 gph or 1098 gph / 60 minutes = 18.3 gpm
Or
3,785 + (372 x .998 metric tons) = 4156 lph or 4156 / 60 minutes = 69.27 lpm
This is the [u]minimum power-driven pump capacity [/u](manufacturers rated capacity; weve allowed for 40 percent efficiency) that should be fitted. If you have less capacity, get a bigger pump or an additional one.
To avoid large amperage draw on the batteries, install the larger high capacity pumps on pads to lift them about 4-5 inches (100-125mm) above the lowest point in each bilge compartment, with each pumps automatic float switch up on the same level. Small -capacity submersible pumps are located right at the lowest point in the bilge sump in each compartment, with their auto float switches at their level. In this way the smaller, low powered pumps handle the vast majority of routine bilge pumping. This reduces battery draw. In the event of a serious flooding situation, the water rises high enough to trip the upper-capacity bilge pumps.
Hope this helps out.
Heres the latest build and launch photos posted in our boatbuilding forum--Congratulations to all for pursuing your dream! Each of you has done beautiful work and should be very proud...
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I would not have looked at it twice if I had not looked at the guys that are behind them: HDS the French specialists in structural analysis, calculation and design....http://www.hds-design.com/
The ones that follow the blog knows that I dont give much importance to the Cruising Boat magazine boat of the year: the categories are too many, the boats are old news in what regards the European Market the number of testers are relatively small, not all professional and did not test a huge variety of boats each here because the boats available on the American market are not many.
