"Rocket" Hydroplane Build

[water_buoy]

Having though realistically about what was to be a Barrelback build I have decided to go with a more sensibly sized (and priced) build. Progress is going well so far and I thought I'd give some info on the boat I'm now doing.

"Rocket" is another design by William Jackson who's boats I have now built three of and from a brief search on the internet I am pretty sure this one hasn't been built before other than the odd few rc versions.

The design is a 15' step hull hydroplane which takes an inboard engine of 45hp upwards. It seats two in the cockpit at the rear with just a long foredeck in front of the occupants
The original plans spec 3/8" hull and 1/4" deck of painted ply but I am planning to go for a cold moulded hull with a mahogany (Sapele) finish, I'm aiming to build it on the style of the 1930's gentleman's racers.

Here's a pic from the plans but as it's only a drawing it requires a bit of imagination!!!

I've sawn most of the frame parts now and hope to have them assembled by the weekend so hopefully I'll have some interesting pics soon. All the other picture updates so far I've been putting on FB https://www.facebook.com/rockethydroplanebuild

[sean-nós]

She is quite close to my crackerbox in looks except for the stepped hull, I hope you go for a bit more than 45 hp If I can help in anyway feel free to ask Haventaclue

[water_buoy]

Yeah quite a similar style really, what is the hull thickness on crackerbox? The plans for rocket suggest 3/8" ply but I'm wandering if I could reduce that slightly with today's more modern materials...

[sean-nós]

I used 1/4" ply and 1/4 mahogany coated in 6oz fiberglass so just over 1/2"

[haventaclue]

feel free to ask Haventaclue

Do you want the man to sink?
But the man to ask is Sean Nós.His Crackerbox is testament to his skill,workmanship and patience .
I had the pleasure of being at the launching,OK,I invited myself ,and it flew across the water without any problems.

[water_buoy]

A few pictures of progress to date...

Fwd 1

Fwd 2

Aft 1

Aft 2

I think I'm going to start assembly with it the right way up, not the conventional way most would do it but it's easier to check the accuracy of everything. The table of offsets in the plans gives a "height above base" for every key point on each frame (chines, sheer, deck c/l and keel) and since my floor is good and flat I'm setting that as base level.
The temporary batons sticking down from each frame at the chines holds them at the right height and perfectly level soo... if I've made the frames properly I should be able to measure the height from the floor anywhere on the boat and it will correspond to the height on the plan.
Once I've fitted the engine stringers which tie into 6 of the 7 frames it should all be rigid enough to then turn over and carry on as normal.

[solitaire]

Dan - when its gets as far as a prop shaft - give me a call - I have a length of 1" stainless shaft with a taper/key/nut on one end - that came of an old Thames launch (it had some wear further up the shaft - (since been cut off) and still leaves about 6ft (probably way more than you need) and you will just need to get the coupling end sorted with a keyway - May help!!

[water_buoy]

That would be great thanks! I think I know someone that could machine it down for me as well I'm not sure on length yet but it sounds like it should be about right. The plans spec a 12° shaft angle but I'd like to reduce that a bit if I can so I've got some calculating to do still.

[sean-nós]

To work out the shaft angle on mine I built a mockup of the hull taking into account the thickness of the planking.



It was a tight fit too get the 1-1 gearbox down to 12 degrees and I even had to shave a bit off it to get it down, the oil-pan was also very tight. You will need to leave enough room between the prop shaft and the rudder to allow prop removal about 4" and a gap of about 2" between the top of the prop blade to the hull.

[water_buoy]

Thanks for that, it certainly looks a good way of working everything out before I go wrecking the hull and drilling it in the wrong place! I'm going with an outboard rudder on a transom bracket so that will give me a bit more room to play with and a bit of adjustment afterwards hopefully.
Did you end up at a 12° angle or something else? Also what diameter prop did you end up using?