PK78 in Central America

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PK78 El Salvador
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PK78 in Central America

Post by PK78 El Salvador »

Found myself in El Salvador in Central America this summer without a boat and I want to explore a few crater lakes and mangrove estuaries. The PK78 seemed the ideal boat. Good rower, can sail, and also small enough to car top by myself and maybe sell as a tender after my tenure here.

There is very basic boatbuilding equipemnt here, so expect a very "agricultural" build. There are some things I have brought from Europe is 6 litres of epoxy, pintles, an old acorn dinghy lug sail and inspection hatches. As I will be single-handing I would like two flotation tanks. The masts I am hoping to make from bamboo.

Will keep you all posted on progress - the idea is a quick cheap build that gets me out on the water.



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Cracker Larry
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Re: PK78 in Central America

Post by Cracker Larry »

Welcome and good luck! Keep us posted, with pictures :D
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PK78 El Salvador
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Day Uno

Post by PK78 El Salvador »

Day one spent finding cheap plywood and lofting - well the instructions say it is not "lofting", so I will call it tracing - but proper use of a bendy batton is lofting in my book.

There are a few issues regarding a few omissions from the plans that would have been helpful, such as the daggerboard case in the central thwart. Its OK as I will make my own design for this, as my sail plan will larger than normal, I think I'd better have a deeper dagger board.

Also, through experience, I know I will get a wet bum with this design. So had a look at making the case forward to the thwart, but decided against it on structural strength grounds; I have a natty idea of making a false thwart above the exisiting one, which one can hinge over the case to stop wet bum syndrone.

A bit more running around for bits tomorrow. Certainly the one hour allocated to trasferring the design onto the plywood is VERY ambititous. Double that!

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Re: PK78 in Central America

Post by PK78 El Salvador »

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Just a quick update.

Photo showing the storm drain I am using to cut the plywood up. The jigsaw is borrowed. I dont want to buy ANY tools so I need to be resourcful. Atlast I have 3/4 of the dinghy sanded (by hand). A circular saw would have been a better bet, but a lot of sanding has never done anybody any harm. If I am lucky and don't have too much on tomorrow I will try to assemble the parts.

I show a picture of the plans as I have a 48sq ft lug sail that a friend has given to me - as there are no sailmakers here so I am obliged to use it. As you see there is a WHOLE lot more sail area than the design spec for this boat so I am increasing the daggerboard depth, skeg depth, and will upgrade the scantling for the mast (hopefully bamboo in Polynesian style). I was thinking of bring the daggerboard forward a bit as the sail makes the COE come right forward, and hoping that might help with balance.

PK78 El Salvador
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Re: PK78 in Central America

Post by PK78 El Salvador »

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Well today I managed to get the dinghy stitched and taped. If working alone, then stitching is the only way to hold the thing together, but it is more work in the end as the stitches will need to be removed. I would recommend just taping the thing together with the aid of a few well placed screws; this requires a second person though. It will produce less work in the end as filleting around stitches is a pain.
I managed to finish filleting and taping half the boat with the help of a very interested 23 year old gardner. He wanted me to show him this new stitching technique and I let him muck in. The result are rather messy fillets, but hey, this is designed to get me sailing and not a work of art. If I can show locals a few new skills on the way so much the better.
The slow tropical hardner is not that slow. Three mixed pots exothermed in just a few minutes. I suppose over 30 degree heat and 100% humidity is not condusive to epoxy work. So managed to tape half the inside of the boat. Tomorrow the other half of the inside after work I hope. Then we flip it and start taping the outside.

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Re: PK78 in Central America

Post by Dog Fish »

Wow, your really moving right along, keep up the good work and the pics. Nice :!:


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Re: Day Uno

Post by Charlie »

PK78 El Salvador wrote:
There are a few issues regarding a few omissions from the plans that would have been helpful, such as the daggerboard case in the central thwart. Its OK as I will make my own design for this, as my sail plan will larger than normal, I think I'd better have a deeper dagger board.
Changing sail plans is not something to do on a whim.
The bigger sail moves "center of effort" of the sail . That will make the boat handle differently. I am not plugged in enough to say if it will be harmful but the center of effort has to be within certain limits in relation to the "center of lateral resistance"which is on the dagger. Ideally, your daggerboard doesn't, necessarily, have to be deeper but in the proper fore and aft position to maintain horizontal "lead".
The sail you sketched looks like a balanced or dipping lug. If that's what it is your mast will have to be a lot taller.
One of the ways around the center of effort problems is to use a sail that has a higher aspect ratio. That is taller but not deeper. That's why sailboard sails are often recomended as optional for these small hulls.

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Re: PK78 in Central America

Post by gk108 »

Charlie has a good point about the daggerboard length. Increasing the sail area will increase the heeling effort on the hull. Lengthening the daggerboard provides more lateral resistance and moves the center of that resistance down, making the heeling effort even more effective. You can get to a point where the boat is easily knocked down, instead of gently heeling over and making a little more leeway. Fore & aft positioning of the daggerboard is primarily determined by the CE of the sail. Size of the daggerboard is very dependent on the size and shape of the hull. Sail area may still go into the equation, but it is not the most important factor.

On the V10, original sail area, daggerboard dimensions and rudder dimensions are very similar to those of your boat. I increased sail area to 40 ft², but left the daggerboard and rudder the same as the plans. In a puff of wind, the boat heels over and spills wind from the sail in a (usually) comfortable way, but it still tracks well. With a longer daggerboard, it would heel over and spill the wind earlier, in lighter puffs. That would mean losing power from the sail when it is not yet necessary to de-power in that way. If you look for it, you can tell that the boat makes some leeway, but that's just how dinghy's sail most of the time.

You could try a longer daggerboard, but be prepared to trim it back to something closer to the plan dimensions.
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PK78 El Salvador
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Re: PK78 in Central America

Post by PK78 El Salvador »

I am certainly making modifications on a whim.

As I have very few resources here, I am obliged to use the sail I brought back from the UK, so best start thinking about how to make the sail accommodate the hull, rather than vice-versa. After a bit more thought, and chatting to a few friends, I think the biggest alteration will be to move the daggerboard further forward by half a foot or so to sort some of the COE and CLR issues. I will make the daggerboard longer but that is not a terminal alteration as I can trim it later. I don't want to alter the sail as it is from a lovely Acorn (Oughtred Design) dinghy - and I would like to re-use it back to the UK!

The mast will be quite a bit taller, but as have decided upon bamboo it lighter and stronger than spruce - so that should be OK. Sheeting ange might be an issue - so maybe a bumpkin will be in order. That can be added after trails though.

I'll let you know how I get on. I only have about a couple of hours max a day to work on the thing at present, so my build has slown down quite a bit. I'll get the hull sorted before I contemplate modifications

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Re: PK78 in Central America

Post by PK78 El Salvador »

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Quick picture update. Undercaoting the boat now using Epoxy primer to line potable water tanks. Seems to be doing the job. end stages now. More pictures soon.

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