lightest scantlings for a s&g tender

[peterchech]

Well I went and did it. Found a 25 foot plastic boat at a price that I could never beat by building it myself. Logic must prevail sometimes...Good news is, I need a dinghy for it. An 8' inflatable weighs about 60#. Well I want to build a nymph (because I have the plans already) , I want it to weigh less than the inflatable. I was thinking to build it of 4mm okoume sheathes in 6 oz glass. Is this going to be stiff enough for a tender that will be rowed, sometimes heavily loaded?

[wizbang 13]

You probably do not need to glass it. Even the filets.Use lottsa curves.
Of course, the boat itself can be very light, but the bits, the seat, floatation, rubrail, add up. This pram was all quarter inch. coulv'e easily used 4mm for the sides.

[k4lmy]

How about the particulars on the pram? Design? size? Weight?

TIA Henry

[JimConlin]

A Nymph of 1/4" okoume, sans glass, will be light enough.

[JimD]

Tell us more about the plastic boat

[peterchech]

Hunter 25, 2'11" draft fixed keel. In good shape, really needs no work anytime soon. It was listed a few months ago for 5900, I think there is just no demand for sailboats these days because if got it for $3400 including the slip until april. Its my first "big" boat and im really excited. I figure ill store the dinghy on deck and tow it when sailing, so it needs to be light and capable of being towed above its hull speed.Seriously though, the lead in the keel alone is almost worth what I paid for the entire boat...

[JimD]

Hunter 25, 2'11" draft fixed keel. In good shape, really needs no work anytime soon. It was listed a few months ago for 5900, I think there is just no demand for sailboats these days because if got it for $3400 including the slip until april. Its my first "big" boat and im really excited. I figure ill store the dinghy on deck and tow it when sailing, so it needs to be light and capable of being towed above its hull speed.Seriously though, the lead in the keel alone is almost worth what I paid for the entire boat...

Sounds nice. Lots of similar deals around here, too. I've been tempted but have held off. Not the right time for me. What year?

[peterchech]

1981.I mean I may regret it when I have to find a place to keep it next summer but I think I can get a mooring permit and install my own mooring somewhere and then keep it on that hook year round for free, after that initial investment.Alot of non sailor friends have gone out with me on my open boats, and not come back. They were either scared or uncomfortable. And the ability to comfortably overnight will be huge for me. Anyway, I found free plans for "apple pie" on duckworks, a 7' flat bottomed dinghy. Ordered epoxy already. The single chine may be even weaker if done in 4mm...

[wizbang 13]

Ya, flat bottom, even with a bit of rocker, makes for a wobbly bottom.
Have you seen how I do my wee prams?(I dint invent it). The bottom stiffens up nice.

[peterchech]

have any plans wizbang?

[wizbang 13]

No plans. I build cardboard models, 2" to the foot, using numbers (length, beam at top n bottom, etc) from established boats, usually my brides El Toro.
The" compound curve / dart thing on the bottom", has been used by me on at least 20 boats, oar,sail and power.
The temp board going across the middle with the threaded rod controls the deadrise in the middle. Y'wanna keep it pretty flat there for initial stability.
What ever cardboard ( mattboard, not corrigated) will do , so will ply. You can customize your pram for your mothership easily. For instance, the cutout in the transom of the dink from post #2 is for going around a mast when she is upside down, not for outboard protection.
Here is the bottom of a different pram, built in a dusty dirty parking lot over a weekend. I use softwood, a cedar usually, for the clamp/rubrail. And I have done away with skegs on my small boats, for weight. (also, skegs dig into the sand for beach dragging.)

[Cuyahoga Chuck]

This
http://www.bateau.com/proddetail.php?prod=D5
Has a design weight of 55 lb in the rowing version but has been built to 40 lb by decreasing the scantlings. Because this design is true moncoque there is plenty of internal support if the pieces are produced in 4mm and 6mm okoume rather than 6 and 9. Also,if the seat assemblies are glued up airtight they produce more than enough floatation to make the boat truely unsinkable.
The designer built the original of this design decades ago for his own 40 foot sailboat. The pram was used for many years in the Carribean and the designer attested it was grossly overloaded with people and/or supplies many times to the point that the only way to make it go was with an outboard motor.

[peterchech]

That is really interesting wizbang, I may have to give it a try. Looks like you're just using fir plywood there. What is the length/beam of your little prams? What is the weight, approximately? Are you able to manhandle those things over the gunwhales of your boat, without banging it all over the place?

[wizbang 13]

Ya, the "parking lot " boat was built of clapped out fir that was left over from house construction in the Virgin Islands, like most ply there , it is "treated".
The boat in the earlier photo is okume.
The length n beam is whatever you want it to be. Custom prams tend to be a little of this and a little of that to fit the big boat. (I have one of doorskins that is about 4' long).
I can and do whip boats up on deck. And the beach.