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Author Topic: New stepped hull design...advice/comments?  (Read 2160 times)

dougal

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New stepped hull design...advice/comments?
« on: January 22, 2018, 01:24:01 PM »

Currently making a plug for a new hull.
It is 1050 x 350mm and a combines elements from FSRV, FE and Deep-V with a full-width step.
No idea how it will go but its an idea that's been rattling around in my head for ages, so no harm in trying!
The first boat will run submerged drive with a side-exhaust 26cc rcmk (I already have one in another boat).
Trim tabs and/or other adjustments will be made as (or if) required when testing begins.
Any advice/comments are welcome.
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CGAux26

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Re: New stepped hull design...advice/comments?
« Reply #1 on: January 22, 2018, 06:08:44 PM »

Just make sure it is plenty strong across the step, lengthwise.  I had a 13 foot stepped boat as a kid, and it flexed badly on even the smallest wave.
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martno1fan

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Re: New stepped hull design...advice/comments?
« Reply #2 on: January 27, 2018, 05:57:46 PM »

Looks good mate but why submerged drive ? id be inclined to go with surface drive. As regards the step my only concern is where its positioned,it seems quite far forward which will help when the boats first getting going but once on plane it shouldnt be even seeing much water where its positioned .Also i wouldnt have put the bottom strakes right back to the transom  as they create lots of lift . Most modern vees tend to have them end a bit before the transom for this reason .  Be interesting to see how she goes and i wish you luck with it,plug looks really well made and been in the boat building game myself i know how much work goes into plug building .Ive had this Double stepped one on and off the building board for a cpl of years now,one day ill probably get round to adding it to my lineup lol .
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dougal

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Re: New stepped hull design...advice/comments?
« Reply #3 on: January 28, 2018, 12:10:03 AM »

Cheers Mart.
Yeah, it really is an experiment pulling bits of everything together and hoping it works ;-)
There'll be more pics soon - the deck is coming on well...at least when the boat dives to the bottom of the pond it'll look good.
BTW I have seen your dedication to helping fellow model boaters on this forum and others. On behalf of 'the hobby', thanks.
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martno1fan

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Re: New stepped hull design...advice/comments?
« Reply #4 on: January 28, 2018, 09:19:47 PM »

Cheers Mart.
Yeah, it really is an experiment pulling bits of everything together and hoping it works ;-)
There'll be more pics soon - the deck is coming on well...at least when the boat dives to the bottom of the pond it'll look good.
BTW I have seen your dedication to helping fellow model boaters on this forum and others. On behalf of 'the hobby', thanks.

No worries mate by all means go for it ,i hope it works out as you hoped and thanks for the kind words its much appreciated .Ill look forward to seeing how she progresses  ;) .
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Davo

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Re: New stepped hull design...advice/comments?
« Reply #5 on: January 31, 2018, 08:33:55 PM »

Putting 'stepped boat hull design' into Google images brings up a whole load of info on the topic. I never realised there was so much science behind it. I have seen early power boats (Miss England?) where a vent pipe went from the deck to the step to introduce air under the boat to help it break free of the water surface.
Not sure if the science percolates down to model boats but give it a try. Looks a good project.
David
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dougal

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Re: New stepped hull design...advice/comments?
« Reply #6 on: February 01, 2018, 03:51:10 PM »

Davo, I trawled through loads of research documents, patents, images and specialist forums before deciding there isn't a perfect formula for a stepped hull (certainly not with my understanding of mathematics!). What I've tried to do is borrow the best bits from several high-performance designs... The hull is basically FSRV style with over-sized strakes from a FE hull and the step is based on PT Boat modelling tests carried out during WW2! The deck is OMRA-style with the exhaust inside the hull, complete with a 1/10 driver (actually a 'Ron Burgundy' doll from the film Anchorman) :-)
I plan to use submerged drive partly because I have some experience of it and I just prefer the way boats look when running with it. My guess is that if I can get the boat to handle with submerged drive, it should be ok for surface drive...?
Both the hull and deck plugs have been given a couple of coats of durabuild glassfibre primer and sanded back to a shine ready for moulds to be made - I'll put up some more pics shortly.
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Davo

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Re: New stepped hull design...advice/comments?
« Reply #7 on: February 01, 2018, 04:19:03 PM »

Dougal,   
Stepped hulls are a science but you seem to have amalgamated all the good points. I have David Tennant (nicely articulated) as a 6" Doctor Who driving my smaller Sea Nymph boats but recently acquired a cheap Action Man for my Sea Queen. However, I think Ron Burgundy may be a better fit; thanks for the tip!
David
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dougal

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Re: New stepped hull design...advice/comments?
« Reply #8 on: February 01, 2018, 05:29:39 PM »

More pics of the build....Ron Burgundy is happy with it so far ;-)
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dougal

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Re: New stepped hull design...advice/comments?
« Reply #9 on: February 08, 2018, 10:07:37 PM »

Mould making progress...
Plugs for hull and deck were finished with 1500 grit wet and dry then t-cut followed by 12 coats of wax. Finally, gloss pva release agent was applied to minimize the chance of the mould sticking (fingers crossed)!
The lay up is two coats of tooling gel coat then 491PA resin with lots of 6mm chopped strands sprinkled in all the corners/sharp angles before a single layer of 300gsm matt. The first layer is the important one - get any air bubbles behind the gel coat and its a world of pain to fill and repair.
The rest is 6 layers of 450gsm matt in regular polyester resin.
Its messy and smelly but satisfying :-)
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dougal

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Re: New stepped hull design...advice/comments?
« Reply #10 on: February 16, 2018, 11:17:04 PM »

First hull and deck out of the moulds. Pics to follow...Slight change of plan - the 26ccRCMK motor is too big. Never mind, I'm off to Weston Models tomorrow to seek advice (and probably a nitro motor) from legendary RC engineer Alan Greenfield :-)
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Martin [Admin]

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Re: New stepped hull design...advice/comments?
« Reply #11 on: February 17, 2018, 02:55:07 AM »


Did the first 'pull' come out cleaning?
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dougal

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Re: New stepped hull design...advice/comments?
« Reply #12 on: February 17, 2018, 08:34:04 PM »

Yeah, the pva release worked, the finish is shiny and the surfaces appear straight and true. There are some small imperfections in the gel coat on the deck moulding but nothing serious - there was a problem with the pva film while i was already committed with the gel coat so i had no choice but to finish laminating and hope for the best! If the first boat works I will iron out any flaws for the second.
Had a splendid afternoon at Weston Model Centre resulting in the purchase of a beautiful West 46 nitro motor, exhaust, mounts and other essentials which will be ready in a week. Any failure of this boat won't be from lack of power.  Also, as a plan B, my old boat with the 26cc RCMK can now be restored so I get two for the price of.....no, let's not go there :-)

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dougal

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Re: New stepped hull design...advice/comments?
« Reply #13 on: February 17, 2018, 09:47:07 PM »

Here's boat no.1 ....
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martno1fan

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Re: New stepped hull design...advice/comments?
« Reply #14 on: February 20, 2018, 06:02:22 AM »

Looks good so far ,personally though id do away with the flange and but join the parts and go inside with glass cloth tape it makes for a nicer look in my opinion but you can leave that for the next one and see what you think .Other than that it looks good ,what does she weigh ?,id say 7 -8 lb would be a good weight to aim for once joined .If you do stick with the flange a good way to join them would be PU adhesive like tiger bond or sikaflex and back it up with glass and resin inside but having used that adhesive before its not really needed its dam strong stuff ,i joined a hydro years ago with it and it held up to some serious abuse .Or you can go with the traditional method of glass and resin  :D .

https://www.ebay.co.uk/itm/Sika-Sikaflex-552-Pu-Adhesive-Cartridge-300ml/152803955432?hash=item2393d352e8:g:-VEAAOSwGwlaGzR4
cheaper version but works

https://www.ebay.co.uk/itm/PU-PANELBONDER-SEAM-SEALING-ADHESIVE-FLEXIBLE-SEALANT-BEATS-TIGERSEAL-SIKAFLEX/281387875774?epid=1588580459&hash=item4184063dbe:g:374AAOxyA9dSZ-B9
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dougal

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Re: New stepped hull design...advice/comments?
« Reply #15 on: February 20, 2018, 10:04:54 PM »

I'm considering a new deck design if the hull works ok...either way, the second boat will be better finished and details such as the hull/deck join improved. Having a large stockpile of over-ordered glassfibre material I will stick with it for now rather than buy any new adhesives (no pun intended). Just thinking out loud, if I want to make another moulding I could look for a (reasonably local) plastics factory/workshop and see if it could be vacuum bagged...what do you reckon?
At the moment the boat weighs 6lb 4oz (without the legless Ron Burgundy doll) which is heavier than it needs to be but I was keen to get it out of the mould without damaging it.  Also, I added some reinforcing patches across the step.
Alan at Weston model centre was very helpful and tactful - I'm not sure its what he would have built himself but he understands folk do this stuff for pleasure!
Next job is to fit balsa bulkheads (with the grain vertical/perpendicular) to create buoyancy chambers and stiffen the structure (although with the heavy lay-up its pretty stiff anyway). After that the engine and running gear should be ready for installation.
I'm going with simple 2 channel control initially but have a 6 channel tx/rx so more can be added.
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martno1fan

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Re: New stepped hull design...advice/comments?
« Reply #16 on: February 21, 2018, 06:33:11 PM »

You shouldnt need any bulkheads if shes well built mate , for buoyancy many guys use poole noodles cut to fit where possible,these work quite well and dont weigh much .
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dougal

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Re: New stepped hull design...advice/comments?
« Reply #17 on: February 26, 2018, 12:28:26 AM »

Not much boat building last week due to illness but have been doing some thinking...
The hull and deck are really heavy and there are some blemishes I could do without.
So, now I am confident the moulds release I have started tidying them up ready for a much lighter lay-up. I will have to buy some more gelcoat but otherwise intend to use the existing stock of 300 and 450gsm mat with regular general purpose resin. I'm thinking of a single layer of mat, reinforced as required, rather than 3 layers + reinforcement from the start...? The budget could stretch to something like woven cloth if the improvement is worth the cost.
Any advice on the best use of these materials would be welcome.
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dougal

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Re: New stepped hull design...advice/comments?
« Reply #18 on: March 09, 2018, 08:05:48 PM »

Progress! Much lighter moulding - one gel coat, one layer 300gsm matt, hull and deck, plus one layer 300gsm cloth on hull. Ironed out some small flaws in the moulds and have a smooth, air bubble free result.
Beautiful 7.5cc motor, rubber mounts and pipe.
Running gear to follow - direct drive, straight shaft.
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dougal

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Re: New stepped hull design...advice/comments?
« Reply #19 on: March 11, 2018, 09:37:30 PM »

After a few years away from model boating I was sad to see Propshop has gone out of business.
Has anyone else taken it up?
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