1960's speedboat conversion

I have a project on the go converting this boat into a fishing boat.
I have had some good advice on changing the transom height from members,[Par in particular] I am replacing all the timber,apart from the "set in" stringers in the hull.I am a bit concerned about completely removing the gunnels,as this will leave the hull sides floppy,and maybe lose its original shape,which might lead to a twist in the hull.My idea was to measure the length of the old ones before removal,then fit the new ones in their place.
I think the hull has been gel-coated at some point,but it is cracked and crazed throughout.I have sanded a small area,and it comes up smooth,I havent got a clue on how to re-paint it,or what paint or gelcoat to use.I used a heatgun to remove the gelcoat off the stern before I cut the old transom out completely,there is red undercoat/primer showing underneath.This is a home project that I will have to do personally.
Any more advice will be gratefully recieved.
Best regards

 

Generally, when contemplating major renovations, you have to consider "keeping what you got" in regard to the shape. On small craft this could be as simple as a couple of 2x4's dividing the hull into thirds, about equally spaced along it's length, tieing the hull sides together as things are removed and replaced.

Sometimes, depending on what you're removing, you need more reinforcement, braces, etc. to hold the boat's shape. These can be plywood forms on the outside, screwed through the hull from the inside, to insure it doesn't change shape as things are removed. Internal "X" braces are not uncommon as are strips of plywood nailed or screwed to the exterior, all intended to hold the shape where it is.

It depends on what has to come out, their locations, the overall condition of the boat, etc. Post some pictures (we're image whores here) and we can take a look at what you're up to.

 

Old 60's speedboat

Thanks for the reply Par,and the advice.
My boat is sheeted up at the moment,and I have a few pieces of Mahogany in it,along with a few other bits and pieces.We have had a few snow flurries here overnight.I will send some pics. ASAP.
We are at the best end of winter here in the UK,so I can send updates as I progress through the job,if thats ok.
I have aquired some 0.75"marine ply that has fibreglass on both sides [glass reinforced ply] I intend to double laminate the transom out of it,and re-deck with it,then f/glass the deck in using f/glass tape and resin.
I suppose when I send the pics.it will be easier to explain.
Best regards

 

How's the conversion going?

 

Hi,I have chiselled out the rotted pieces in the stringers,I am replacing them with tanalised strips of timber,then covering them with strand glass and resin.On top of these I am adding 5 new stringers,the centre one being 55mm,the two middle ones at 40mm and the two outers at 25mm.These heights give me a level for a flat deck,and allow water passage under the deck to the stern,[if I ship any of course]I am stopping the deck 6" short of the transom to allow for a bilge pump,then overlapping the deck 6"and covering the gap of 6" bang against the transom for support.
There will be vents in the deck at the stern to allow any surface water into the bilge/under deck.There will be an emptying bung low down in the transom below deck level.
The hull is higher at the bow,so I intend to step the deck to suit,this should give me a dry storage area under the fibreglass bow covering.
I intend making a lightweight cuddy with three sides,front,port and starboard,these will be3/4 grp,sawn with a fretsaw and be mainly window,the roof will be fibreglass sheet.
I have recently aquired an 18hp evinrude longshaft,so I will tailor the transom to suit.I intend to fibreglass the deck in.The tricky bit will be maintaining the hull shape when I replace the gunwhales,PAR suggested temp.cross members to hold the shape,which sounds like a good method.
Best regards

 

Sounds good, can you provide some pictures?

Be careful you don't add too much additional structure, with the thinking "it'll be stronger". This is a classic small boat trap and can quickly kill the preformance (speed) and ability (capacity) of a small boat. Think light and strong, not massive and hefty as you place pieces and add your cuddy.

I don't spec anything but long shafts any more, as I consider it a safety feature to have the extra 5" at the transom cutout. Make the ventilation plate even with the bottom of the boat, when you're figuring out the cutout. The cutout should also be about 30" in width, to let everything "swing".

 

Hi PAR,
I aquired a long shaft on your previous advice,it is tiller controlled,so you have saved me a lot of figuring out and measuring with your advice about the size of the cutout.I am considering a short splash shelf at the transom,so I need to consider the swing and clearance for the tiller arm.
I intend to fit short lengthways seats port and starboard at the stern to give access to steer the boat.
I have considered the overall weight,and intend to keep it as light as possible,the cuddy will be more of a lightweight framework,with the window openings recessed to take perspex windows pressed into sealant,then covered with a sealing strip externally.Unfortunately fixing the sealing strip will show the fixing screws,[stainless] which I hope doesnt look too "un-professional"
At a rough estimate,without the engine,I think the overall weight of the boat will be around 500/550lbs,inclusive of gas tanks,anchor and ropes etc.
The engine is a 1964 18hp evinrude fast twin,it has been recently overhauled,and never been in seawater,which reflects in its cosmetics.I am bit unsure whether it runs on 50/1 or 100/1 gas - oil ratio.
I have yet to design s/steel safety rails,I thought maybe a 15% outward leaning pitch might be advisable,this would give a grip rail for passengers when under way,and a safety rail to add height to the sides when moving about in the boat,plus a fixing point for rod holders.
I haven't fitted the transom back in yet,I am unsure whether to fit the stringers and deck first so that I have easier access to the inside of the boat,
I would f/glass the deck in after the transom is fitted.I'm a bit unsure if this procedure would interfere with the hull form/shape.
I will send some pictures later in the week,there's not a lot to look at at the moment.
Thanks for the advice,
Kind regards