Puddle jumper MK2

hi all i am in the process of building a MK2 and would like some help on the size calculations
i found this . . .

 
i have tried to work out the dimensions for a 11" propeller and a size .90 engine
could some one go over my calculations for me (i am not so hot on maths )
and let me know if i have gone wrong see below

I've written out what i believe to be the right measurements and calculations based off your 11" prop and made a couple of adjustments to what i think is better suited for a model of this size. 


Note ------- i think this plan is based on a prop no bigger then around 6" going off the drawing looks which can explain a few issues you  may encounter at scaling it up larger


However

DON'T TAKE THIS AS GOSPEL!! RECHECK IT SEVERAL TIMES I DON'T WANT TO BE BLAMED FOR INACCURACY'S!


Others may have better suggestions!
 
A =11" prop + 1/2" clearance making 11.5" or 5.75" to motor shaft center.

B = i believe it should at least 2"  but you could go up to 3"!! ( remember thats a huge 11" prop and boat, you'll need buoyancy which i don't think on a boat this size 1" will be enough to keep the arse out of the water??!) 

it states angled out sides i would look about a 10-15 degrees would be enough. be aware this will make one of the panels bigger then the other, i suggest top panel to be 16.5" wide and the base panel to be the degree ratio smaller in width. 

Width = 16.5" ( remember its 1.5x prop which is 1.5x11=16.5, you had it at 17 and a quarter) 

rest I've written on the plan....to my understanding of each dimension.

but it works out that the boat being 16.5" wide and an overall length of 33.5" ( which is almost the 'golden ratio equation for a rectangle, being 1:1618 better knows as 1:PHI)

quick note when converting inches to CM/MM  watch out for the 0.0'S!!! cos those will not translate correctly, you will have to work those 0.0's sepratly into cm/mm and add to the whole number to get the correct conversion.

0.5" is 1/2 inch

0.75" is 3/4 inch

0.25" is quater inch

but 0.4 is almost half inch! but its more like 3/8th!

WOW!!!  thanks guys you have been a great help
just goes to show i am in need of a maths teacher lol
seriously a great help
i like the spray rails idea these wont catch when in a turn and flip the boat?

P.S
i have looked at them on google but i would not be sure on there placement and there size and shape
good idea though

honestly i wouldn't have thought so if they are rounded over a little on the sides, they are used on most sports boats but honestly i don;t know how they effect air boats... I've never built one but have seen them on many photos over the years, some hulls are actully moulded or formed with little ridges in 

 i think they are used for allowing the boat to run straighter at higher speeds, my advice would be to use something like 5x2mm lengths maybe put 5 on at eaqual spacing. again research on google for more information.

I know how you feel with the maths Goldslinger fortunately I married a teacher.

I built my 2 airboats much too big for the brushless motors I used and they're quite slow on the water good for when the grand kids visit though.

Damien.

Roadrunner thanks for your help on the design plans
in the end i went for a 2 1/2" hull height
which meant extending the total length by an extra 1 1/2" sorry to mess up your 1:PHI
also i thought a 10-15% angle was just a bit too shallow i tried various angles
(on the drawing /kitchen table) and they just did not seem right so i compromised with a 35%
i also tapered the bow by 1/2" from the 2nd to last cross rib taking 1/4" off each




sorry the pics arnt so good they are pencil drawn and don't show up so well

Good start, yes u would have needed to adjust the rake angle for the increas in height as for the angle I just looked at what real air boats look like and opted for something realistic in looks, most are pretty much flat or if they have angles are very shallow, again I just used some judgement of course your own opinion is what matters. I just hope this boat puts you in good stead. 

A note on keeping the hull water tight... My advice would be to put in strip wood 5x5mm around every butt joint, this will ensure a better glue joint for strength and waterproofing.

Once glued up also go over the joints with car body filler and sand smooth. This again will ensure no gaps and allows you to true up the panels without adding much weight ( filler is dead light) or you can use some resin which will add weight. Both methods are fine, body filler is much cheaper and less messy. It's also good as a glue!!!

And just a quick note before you start painting you should seal the wood inside and out ( fuel proof it) the best way to seal wood is to use either sand sealer( but note it could react with the top coats of paint, some acrylics can develop crazing later on as of the paints literally sliding about the surface) but I've found the best method when any paint is the final coat to seal using car laquer, use two decent coats and let it penetrate the wood to seal, light rub down with 600 grit then on to your primers and top coats.

Hi Roadrunner
i think i must be thinking more of the swamp boats which appear to have an almost vertical side to them but as you say its down to personal taste
on the the point of sealing the seams last time i used uni-bond hard as nails and put a 1/4" bead all around on the inside as it has that bit of flexibility plus it is waterproof and sticks stuff so i might go down that road again good suggestion though
to seal the rest of the hull on the inside i gave it one thin coat of fiber glass resin just to seal the wood and on the out side i gave it a thin coat of fiber glass resin again just to seal the wood and give me a smooth surface to work from this was then rubbed down with 2000 wet&dry then i did two car spray primer coats then rubbed those down with 2500 then two top coats of car paint a final rub down with 2500 and a final coat of resin to give the paint some protection from knocks and bangs

PS the last air boat (Puddle jumper)leaked because i moved the engine and control box forward
(to try and get the d$m thing to sit level) so nothing lined up properly
i think i have sorted the leaking by using draft excluder on all the new joints IE the control box hatch servo rods etc
all now appears to be water tight but it is still way to heavy for its size i need under water cameras for it lol

Take a look at these photos if your worried on hatches leaking water, 

Its best to create some sort of combing or secure the hatch gaps with hatch tape/ screws/Vaseline or a combination of things..

This build blog (below) of my most recent project actually uses 3 different types of hatches for each particular section on the boat.( its also worth the read) 

https://www.thercmodelboatforum.com/t1272p50-row-row-row-your-boat#11961

I've added a few photos of combings and hatch sealing methods that are very effective, the last photo of the yacht however is the most fool proof and will never leak and makes that boat virtually air tight!
( that yacht build is linked below which dose show how it was built up)

https://www.thercmodelboatforum.com/t887-wee-nip-build

there are many more ways to seal a hatch, these are just the few i do use that i know are very effective regardless of size or position!




 



and just another photo shows the same type of hatch seal can be created to give you a flush deck, here is a photo of another yacht the same as above i was asked to build for someone earlier last year.

the hatch is exactly the same in the way its constructed its is just inset into  the hull to allow the hatch to become fully flush, and a screw lid ( its off a dogs medicine bottle) the threaded section was sliced off and inserted into the hatch and simply using the lid to unscrew to gain access to the battery and on/off switch for simple use, leaving the hatch permanently sealed and screwed in place and only removed for maintenance.

you have some nice boats there and as you say there are lots of ways to seal hatches
originally this has a raised lip on the inside which worked well
the problems started when i had to move the whole lot forward including the engine mount
which is now over a gaping hole
so a bit of rubber,car body filler and some draft excluder did the job
MK 2 will be a nice tight seal

thanks off to the pond later to see if i can drown the servos again lol

well got down to the pond for a splash around and every thing was going great the engine was running well no water into the control box yahoo every things right with the world then . . . . . .
oops i lost my footing then my balance on the cobble shore i dropped the remote to save myself from a soaking
and the air boat went full throttle into the sluice run off wall splitting the front of the hull from the deck ripping the engine mounts off the hull and the fan guard was thrown into the propeller taking clunks out of the blade and bent the servo rod to the rudder
oh what a day serves me right for being so bl**dy cheerful

An ooooh darn moment.

Oh dear doesn't sound good, can it be repaired and live another day ?

I think I would have rather fell into the water than ruin all that hard work but it could have been worse, the controller could have taken a dip and ruined that too, commiserations to you and hope you can sort it out so it's not all lost..

That's the problem when running engines when something goes wrong they always go wrong in style!

can we get a photo of the damage? i haven't seen something destroyed in quite a while!

Be sure to fit a fail safe on your mk2 to avoid something like that again.. shutting the throttle off when the sh*T hits the fan ( literally in this case) might save the model should the worst occur again.

As another suggestion i use a transmitter strap around my neck ( its actually an old camera strap i tied off on the transmitter), so if i need my hands free (or i go tumbling)  i can drop the transmitter and it will just hang in place. ( bit of cord will work just as well) 

That said i was only a couple of years ago i dropped my transmitter in the drink even with a strap fitted, point was it wasn't around my neck at the time! i can only laugh now at that moment but at the time i was pretty peeved, fortunately it wasn't my spektrum set and happens to be a bog standard 27mhz set i was using. ( something said for using cheap equipment its not so hard on your wallet!) 

we all feel for you when something bad happens to your hard work its such a depressing moment.

Earlier last year when i was in hospital one of the club members had their tug boat sank in a freak incident when one others members model ran full astern ( i guess he wasnt paying attention and knocked the stick full back) into the tug, capsizing it, knocking the superstructure off and instantly flooding the model.
Efforts were made to attempt retrieval but it was sadly lost at sea!

The tug was retrieved from the bottom of the lake earlier this year tho when the lake was drained)  but its nothing but scrap after a year in the salt water.

Ironically the same member also the year before last lost his IOM in the lake when the hull sprang a leak( the story was his dog knocked it over at home and it must have split a plank or two, to which the damage wasn't spotted) . That boat fortunately was retrieved as the boat hit the bed the mast was still sticking up outta the water. I guess you could say some people don't have much luck at times.

Been there middle of winter  a strong squall hit my Schooner Emma C Berry laid the sails flat on the water where she stayed until a hatch cover came of and she went down quickly about 100ft from jetty top of masts just visible in the troughs of waves stripped to just jocks and shoes Had bronchitis for months afterwards.

well here is the live footage of the crash
good job the pilot was wearing his 4 point harness
both his arms and legs were straight out in front of him with the force of the impact lol






i have already started repairs so there isn't much to see on the hull now
but the engine frame work and fan guard are little bit bent
the rudders are missing as i took those off for the rebuild

OUCH

Glad to see you are rebuilding the boat   The rock edging to the pond doesn't look very forgiving

the rock edging is only at the exit sluice to the pond most of the rest of the banks are dirt
i just pic the best spots to crash at full throttle
the rebuild is coming along but it wont be as good as it first was but it is a good one to learn on
as i am about to start the MK 2 which now i have got the correct dimensions will in fact be a huge 35 incher
with a whopping great 60 engine and an 11" triple prop all singing all dancing beast

goldslinger wrote:

as i am about to start the MK 2 which now i have got the correct dimensions will in fact be a huge 35 incher
with a whopping great 60 engine and an 11" triple prop all singing all dancing beast

I am really looking forward to this one  

what a mess
the bow was easily fixed with some filler and a bit of paint
but the propeller guard well that's in the bin along with the engine mount
it was all too badly bent out of shape to do anything with
i made a new engine mount from a couple of blocks of wood
and replaced the fuel tank with a standard tank and mounted that parallel with the carb
as i was having probs with the fuel mix going from rich through to lean as the fuel went down in
the barrel
next was to sort out the mounts for the rudders this was a 1"x1" piece of wood cut in half
diagonally down the length giving me two triangular supports for the rudders with bracing across
the two and diagonal supports to help  stabilize everything
last to sort out is the propeller guard for this i thought i would have a go at bending some 3mm carbon fiber rods
just to see how far they will bend as i want to use these on the MK2
and i was surprised to see i could bend them into a 10" circle
that's it basically a touch of paint and all done and working
when i have time i will take it down the pond for a splash about