Three Views of the Pram
Why The Pram...?
The pram type
makes an excellent tender for any yacht, having the most carrying
capacity within the least length compared with any other shore boat
type. We have developed four basic pram designs at 8 feet, 10
feet, 12 feet and 14 feet. Each of them share the same features and
general shape. The ten foot pram is shown in the drawing above.
Intended for
construction in welded aluminum, these little boats are easy to
assemble. They are light and extremely tough. As a further
advantage of welded aluminum, these prams have built in flotation
compartments for unsinkable safety. A longitudinal WT compartment
is along each side, plus the aft seat and forward seat also are WT
compartments.
Check out the following photos of the 10 foot pram built in Port Townsend, Washington. These pics were taken by Lena
Kasten on the pram's launching day in Port Townsend Bay.
(I'm the guinea pig in the yellow life vest..!).
The Pram In Use
Sailing:
These prams are all "Cat" rigged. They make use of leeboards in
order to keep the interior clear. The presence of the leeboards on
each side is the very reason for the topsides to have a generous
tumblehome – so the leeboards will naturally have the correct angle to
the water on the leeward side when heeled.
You can see from the
photos in the above links that we did not have a blistering sailing wind
that day...! Sail we did however, plus we had oars...
Rowing:
Just the right amount of rocker has been given to the bottom to allow
easy rowing. Due to the bottom rocker it is not an ideal craft for
planing speeds or high power. Sailing and rowing however are excellent!
Motoring:
The aft transom rakes aft a bit and is designed to easily take a rudder
for sailing. We have created an outboard bracket (detailed on the
plans) that mounts right onto the rudder gudgeons. The outboard
bracket is very strong and will take a low power "trolling" outboard of
around 3 to 5 hp on the 10' pram, and up to 8 or 10 hp on the 14 footer.
This will provide very adequate displacement speeds.
Convenience: The
forward transom allows one to step right into the bow and the pram is
still stable. This is really quite convenient: The
combination of the flat bottom and the forward transom ordinarily allows
the pram to be driven right up on the beach where one can step off the
forward end and not get thoroughly doused whilst going ashore.
Camping:
The fully welded all aluminum hull is extremely strong, in
particular with the floatation chambers along each side. Thus the
prams do not require the added strength of a center thwart, and the
center rowing thwart is arranged to be removable. The use of leeboards
and making the rowing thwart removable were choices we made primarily in
order to allow a completely clear and unobstructed interior for day
sailing.
However this
combination also allows the 10' to 14' prams to be used for camping
while at anchor or while beached. The bottom is flat athwartships.
Thus, with a sleeping mat laid on the bottom you can stretch right out
in there using the boom and sail as your tent. With a good
sleeping mat, a friendly couple can sleep there quite comfortably.
Stowing:
As can be seen in the drawing below, towing and stowing are also
optimum. What makes these prams so easy to stow? It is
primarily due to having a transom at both ends. Because of this,
for a given carrying capacity the pram is able to be shorter than a
similar craft with one or more pointy ends.
Capacity: In
addition to its own weight, the maximum carrying capacity of the 8' pram
is around 350 lbs. The larger prams have proportionately larger carrying
abilities. For example, the 10 foot pram can carry 25% more weight, or
around 435 pounds. The 12' pram can carry 50% more, or around 525
pounds. The 14' pram can carry 75% more, or around 612 pounds.
Basically, a pram is
able to carry more weight per foot of length than any other type of
shore boat. Well... that is until you consider an
inflatable, but those things can not be properly rowed (you have
to 'pry' them along)... nor does an inflatable offer the fun of
sailing!
8' Pram - Click for Larger Image
12' Pram -
Click for Larger Image
Dimensions & Weights...
The 10 footer is 10 feet end to end at the top
of the transom, and the other sizes are also as long as their
nominal length, from bow transom top to stern transom top.
All the prams are the same width at 4' - 4" to the outside of the knuckle.
Bottom width is 3' - 4" for all of them. Maximum height from transom
top to skeg bottom is 1' - 11" for all the prams.
When finished, the surface areas are as follows:
- 8' Pram: 76.5 sq ft
- 10' Pram: 90.2 sq ft
- 12' Pram: 106 sq ft
- 14' Pram: 131 sq ft
These are the total surface areas of each aluminum pram, as-fabricated.
The weight of each pram size will depend on the thickness of sheet used.
We advocate 1/8" thickness if you will be using a pulsed MIG unit for welding,
however if you are using straight spray arc MIG then 5/32" thickness will likely
be preferred. Weight per sq ft of each thickness is:
- 1/8" aluminum plate: 1.75 lb / sq ft
- 5/32" aluminum plate: 2.1875 lb / sq ft
Add to that the weight of oars and center
thwart (spruce oars and western red cedar thwart, so very light) for
the rowing version. Say 6 or so pounds, plus bailer, nylon 3 strand
painter and shackle.
Add to that the weight of leeboards,
mast, headboard sail, halyard block, sheet, halyard, rudder, tiller for the
sailing version. Douglas fir mast; marine plywood leeboards, rudder, headboard;
oak or ash tiller; Dacron sail, Dacron line. Say 12 to 16 pounds.
You will observe that the weight of the as-fabricated aluminum for
each pram size varies directly as the percentage of difference in
length, adjusted per the thickness being used. The weight of the
other items is fairly close to a direct percentage as well...
however the painter, bailer, shackle, halyard block and similar
items will not vary.
NC Cutting Files
An NC cutting kit is
available for these prams. Please see the
Plans List Page for a summary of the plan and NC kit prices.
What is NC?
It simply means Numerically Controlled... in other words,
computerized cutting.
The NC cutting files
allow plasma or abrasive water jet cutting of all the parts – including
hull plates, transoms, seats and WT compartments. The result is that
construction is very quick since a mould or building jig is not
required. Using this method, I completed all the metal fabrication
on the 8' aluminum pram in 4 days, complete with welded-on fittings.
Why is it so quick to
build? There is no time spent planning, nor lofting, nor spiling of
shapes, nor cutting, nor worrying about any of those things!
When we built the 8 foot pram, to begin we
simply placed the bottom sheet onto two saw horses, pushed the middle
down, fit the side pieces and transoms to it, and tacked it all
together. The basic hull plates and transoms were assembled in a matter
of hours.
In plywood, the same NC
files can be used for cutting the sheets via a computer driven router.
The NC cut parts then simply "stitch-and-glue" together, and again a
mould or building jig is not required. In plywood, the
configuration would be exactly the same - i.e. there would be the same
shape and the same floatation chambers.
How Do You Get One...?
By far the most cost effective way to get one of these prams is to
build it yourself. For that purpose, the use of NC cutting makes the job
very easy and quick.
When pram plans and NC cutting files have been purchased, we will
then provide contact information for several first rate metal cutting
companies who will do the NC cutting to create a boat parts kit, as well
as contact information for a
number of aluminum boat builders who can do the hull fabrication.
If desired, we can also recommend sail makers and spar makers, etc. but
you might want to make the spars and rudder and leeboards yourself...!
We have not as yet detailed plans for other pram sizes. If
other sizes are of interest, we would have to create the plans and the
NC files for that size pram from scratch. For our design work, i.e.
generating the building plans and the NC cutting files, and making the
introductions to the cutters, and builders, etc. our fee will be
estimated on a case-by-case basis. If this option is of interest,
please
inquire.
7' Pram -
Click for Larger Image
In my opinion, 8' is about the smallest practical size for these
prams if any reasonable rowing and / or sailing performance is to be
had. That said, certainly they can be done in smaller sizes, but
at a great compromise in terms of performance and carrying ability.
Also, at smaller sizes, aluminum construction is probably not optimum
due to its weight, and the better choice would be a good quality of
marine plywood...
If any of our pram designs are of interest, the best way to discover
building costs is to obtain the building plans and submit them to a few
builders for a quote.
Please see our Plans List Page for a
summary of the Pram Building Plan and NC cutting file costs and ordering
information.
