R.J. West

I'm in the process of working on my Dumas Pay n' Pak sport 20 hydro thats been sitting around in its box under my bed for a number of years.

I'm building this one with intentions of competing in the sport 20 class. I'm an average hobbist and I dont have a garage turned full blown workshop.
As of right now the hull is framed up and the hull bottom and sponson sides are on. What I've done so far was to use my dremel right angle drive and pretty much made generous cutouts in all frames and stringers in an attempt to lighten it up. So far its going very well..I still have to do the side stringers and any bulkheads that form the center will be removed if they are not needed.
It will be powered by a new O.P.S. .21 side exhaust. I do have the Dumas hardware for this one, it comes with a straight driveshaft, which I dont mind, and I know a few hardcores out there will tell me otherwise, but I do like Dumas hardware. Although I think the turnfin that came with it would work better as a can-opener, so I picked up a neat polished aluminum turnfin designed for 20 size hydros instead.I also have a Hitec MG645 servo for the rudder control. So far I think I'm set.

Couple questions
For racing in this class, what size fuel tank is reconmended? I have a sullivan SS-6 & SS-10.....
Does anyone know anytricks that can be done to the sponsons bottoms? Theres a 1/16 "ride pad" that goes on the sponson bottom inside.
The engine bay measures 3.5 inches wide. I've been looking for a rubber isolated engine mount, butno dice. The Dumas/steve muck designs is o.k., but 4 inches is too wide.
I might be using the dumas hard mount.....

advanced builder

RJ , Go see Joe for a mount 2.58" Overall
http://www.solingerrc.com/index.html

Hydro Junkie

I wish you had asked questions about the boat before starting the build. I could have given you a lot of info as to what you needed to do to the boat, STARTING WITH MAKING IT WIDER. A different bottom profile would also benefit the boat as well as moving the radio box forward of the engine. After building one years ago using Dumas hardware, I would never use their hardware again. I would go with Speedmaster and redo the frames with 1/16th ply with 3/16 ply for the rear transom, include the lightening holes you are doing. Your boat would still weigh less than the kit build and be a bettter, faster boat. This kit isn't up to racing with the more modern 20 hulls and would be better suited as a play boat.

R.J. West

Hi HJ,
I'm familar with the advice you've been giving for the past 4 yrs on this site as well as Intlwaters, and I do appreciate the input, however the advice you give requires investing in some power equipment & and basically redesigning and building a boat from scratch. In that case I wouldve bought some of Newtons plans....

Whats wrong with Dumas hardware?
To me, I see their hardware as a clean slate. You can make changes to it as you see fit. I have seen some fine examples of some machine work done to their struts to lighten them and shape them. However I'm not a fan of using roller bearings in a strut, and their #7004 turn fin is worthless...Looks like something a caveman made to skin a deer.

I have ordered a speedmaster strut and rudder and feel that in the long run aadjustable strut/flex cableis better for fine tuning the ride...
The radio box layout in these boats is outdated, The fuel tank I want to be close to the engine and its staying up in front because I want weight up in the nose, the radio however will be located in between frames5 & 6. Frame 7 in front of the strut area may be removed, but that small little square area that 5 -6 makeup will be the radio box. So that way some weight is eliminated off the tail and moved forward...

Naturally I disagree with the comment that the boat is better off as a "Play Boat". What happened to drivers skill at a sanctioned event? Or having a reliable setup? This is a HOBBY, I am not a trophy collector, although I do have my share....[img]file:///C:/Users/Ron/Pictures/rock2.gif[/img]

Hydro Junkie

To each their own I guess. All the Dumas hardware that I've seen has all been brass, much softer and easier to damage than the 6061 or 7075 aluminum other manfacturers use. The exceptions are the rough cast aluminum rudder brackets, rudder arms and skid fin assemblies. The rudder bracket alone, not having a kick back system, is asking to have the transom ripped out of the boat if you hit something.
Being a skilled driver helps, as does having a reliable boat. Being competitive also requires speed and stability on the water. The Dumas kits are too narrow to be stable, as well as too heavy and too poorly designed to keep up with the newer designs like the Whiplash and PT20.
Why would you have to buy expensive power equipment? A jig saw, drill and sander would be enough to build a boat with. As for a redesign, I would extend the front part of the bottom back to the next frame. Doesn't sound like a redesign to me, just a simple mod to remove that air dam in the front of the boat

R.J. West

Like you say, "To each their own"

If everyone is racing whiplash and P Thomas boats and running CMB 21's then that sounds too much like stock car racing...Makes me even more determined. Whatever happened to "hey R.J.the boatlooks nice" or "Hey, I built one of those" ? Now we're telling each other "Its a play boat".....I would never tell a guy who's boat is better or if this manufactuer or that one is no good. Let me tell you all something. It shouldnt be about money, or who can make a better boat. It should be about passion and imagination. I remember one event yrs ago when guys would put a towel over their boat so no one would see what motor or prop they were using, C'mon....
I know there are some limitations & questionable wood in Dumas kits...But that is where the HOBBY begins...

Theres nothing wrong with Dumas hardware or their boats. You have to look at it.... and build it anyway you like, by usingyour imaginationandmake changes to it as one see's fit, and then say " Look at what I made" instead of saying 'Look at what I bought"...
I remember when usac and cart ran at Indy, and all different manufactuers were involved, now, with that stupid IRL, pretty much the same chassis & engine combinations are involved.


What I'm looking for is if anyone has done a sponson bottom modification thats proven to improve turn stability and wants to share that info here. I only know about using a 1/16 ply ride pad that hangs over an 8th or so into the tunnel to help the sponson cut into the water...
Also what is a good size fuel tank to use? Dumas Mentions a SS-6 but I feel that is too small....

jetpack

My Feedback: (1)

A six ounce tank is standard for your average .21 and if you're going to use a hopper tank that will be an extra ounce or two. A hopper tank isn't a bad idea no matter how close your tank is just because it will have a more even draw at the carb.

I think going to an 8oz. tank would be okay just to be safe but the OPS will do okay on milage with a 6oz unless you plan on feeding it LOTS of nitro.

Fit a bigger tank to be safe I guess, and then from there measure how much you fill it if you want to run just 6oz?

The more current race motors are hungry and take lots of nitro and those guys have been using 8oz so maybe you can judge from there. I haven't run my OPS to know how it's going to do on fuel but being an older design motor with a high compression head I can't see it being a fuel monster.

R.J. West

Its a pretty cool engine, brand new in the box on ebay for 120 bux... I really like how the header design is, ie, side exhaust but the way its designed it leaves me with plenty of room around the engine well and no mods needed to the cowl...I'm still looking for a decent replacement for my old K&B #8060 .40 w/side exhaust thats in my U-76....So far, I'm eyeballin' that Mecoa .46. I tried bidding on k&b .45 rear exhaust but keep losing the bids...

I never ran a sport 20 and wasnt sure what the fuel mileage is on an OPS .21. I thougth 30% nitro would be a good start.Not sure what a good propto start off with would be, I'm thinking maybe a X440-442 & work my way up.
I was thinking about an SS-8 myself, thanks for the input....my ops came with a few replacment parts sheets but no instructions, if anyone wants to share I'd appreciate it. my engines pretty clean and it feels alittle tight up on TDC. I ordered a Mac tuned pipe for it & I'm going to presure tap it. Oh, I also found me a OPS exhaust throttle I may be experimenting with, whats your opinion about using a exhaust throttle?
Any ideas where I can turn to for replacement parts? ie. gaskets & bearings?

As of now I'm just waiting for parts to come in ,hardware andservo mounts. My Klass-Kote #100 white & catayst came in via UPS today. I bought a pint of each and it ran me 10 bux for shipping....

jetpack

My Feedback: (1)

You did good on the price thats what they go for new. Strong motor and last forever from what I hear. Just use a good oil mix. OPS wants 25% castor.

Being OPS, they never packaged anything but a general running instruction sheet with most of these but here is a parts sheet.

I would pull the head off and see what head yours came with. There's a low nitro (EU) and high nitro (US) version. The EU version is the smaller chamber with the double bubble profile. I wouldnt run too high of nitro with the wrong head, the rods are hard to get. Most likely yours will have the large chamber with the smaller squish band.

I like exhaust throttles because for me it is easier to tune a venturi than it is to tune a carb sometimes. If you're a tinkerer you can easily play with venturi sizes with exhaust throttles with the venturi's simple to make. One more step into hands on tuning with these. I have a few of them myself both inboard and outboard types for the 3.5 K&B.

Your carb is the later cast body type which you dont usually see. I have a slide barrel car carb I can try with mine besides the billet carb body in the pic.

I never knew OPS had an exhaust throttle until this week I seen one on eBay. It would be nice to have but I just got laid off and can't bid. Agh!!! I believe OPS even had a megaphone exhaust extractor for this manifold, about three inches long and cone shaped. Not spun, but cast like the manifold.

I'll send you an email with some OPS scans you'll like to have. It's good to see another Dumas build and should be a great boat to get loose with. Glad your going to be the first test subject with the KlassKote. It's the system I decided on for when the time comes and looking forward to your experience with it.

R.J. West

The box says 3.5 speed RCB model # 8770. I pulled the head off and its this one thats pictured below...
I would love to finda OPS 7.5cc like this for my U- 76 because of the exhaust design being out of the way of the cowl...
Thoses some slick photos you have there, I like the outboard...I'm diggin' those older k&b 3.5's. Man I tried bidding on a NIB k&b just like those and lost out....What do you use to polish up the casings and heads?

well, like always I'm putting all effort into my project, concentrating on balance of performance & reliability, with a touch of longevity.....With all the cutouts I made, I really must concentrate on sealing up thoses cuts good without soaking them like a sponge....

Now I used Hobby Poxy and K&B's epoxy paint back in the day and really liked them both. From what I get, Klass-Kote is a similar product. I havent used it yet as I'm debating if I should get one of those Preval throw it away sprayers, or brush the whole boat down.
I used a preval sprayer on my Hot Shot 45 using k&b paint and it worked great......But damm I remember how much of a PAIN it was to try and sand that stuff after it cured....
I havent had the opportunity to brush on an entire boat and wanted to get some iput from others first that have brushed their boats...
My U-76 I told you about is in primer that I wet sanded w/400, its super slick N shiney, can I just brush the whole thing down? I dont own any spray equipment & I'm somewhat of a novice

jetpack

My Feedback: (1)

Epoxy brush paints really well. I think KlassKote has their own set of instructions as to what type of brush to use and mixing ratios, but I remember brush painting my first two boats with HobbyPoxy which is similar to K&B epoxy paint but just a bit more flexable. KlassKote is a little different because I think it is a water based product.

Epoxy paint lays out very well, and making it an even coat thickness is very important and hard to control because it goes on thick but if you can master that it can be as glosssy as if you sprayed it.

Forget about using the same brush twice though, you'll never get the epoxy out well enough. Just don't buy the really expensive ones, and not the cheap ones either...the epoxy really pulls on brushes and it will leave bristles in the paint.

To get the ultimate gloss though with a thin clear coat after wet sanding you'll still would want a spray gun to do it right.

I like the idea of KlassKote being water clean up and it will be great to see how it does brush painting. Brush painting is really the way to go sometimes with less of a hassle and overspray mess.

The OPS head you have is the high nitro head with the larger chamber. Check to see if you have shims under the sleeve also. If so take these out to break it in and find your pipe length and carb then you can start playing with raising the sleeve timing.

For all my polishing I start with using garnet and silicon oxide polishing sticks that are used with a little bit of oil. A tip can be formed to clear out all the sharp inner corners without digging trenches around it, then I use KISS board files found at walgreens for larger flat surfaces, wet sanding all the way. Mothers billet aluminum polish for the high shine, and a stainless steel brush with Barkeeper's Friend cleanser gives a nice satin shine, and is also used to lap in head buttons and backplates and more.

The polishing sticks come in all grit sizes and are very easy and quick to use with lots of control. Once you try them its easy as crayons with excellent results. Tool catalogs such as J&L have them. Look for EDM or Polishing stones.

R.J. West

When I pulled the head off, I also took out the sleeve to clean off minor gumming of the oil and there was no shims under the sleeve.

R.J. West

Nothing really new & exciting to report, I'm still waiting for my hardware to come in....What I've done so far was to seal those edges of all the cutouts I made.

Dumas does use a lesser quaility woodfor the frames and stringers, the plywood that makes up the skins is good quaility birchplywood though.And thats to help keep them more affordable, but as a result the modeler should pay close attention in sealing the wood, more so than aircraft grade plywood. From what I can see, Dumas ply appears to be pressboard or sawdust material mixed with an adhesive and sandwhiched between thin birch or mahogany. Aircraft type ply appears to be thin pieces of solid wood laminated together...

The outside shell of the ply is good, what the issue is the inside of the ply pieces, and all those cuts to lighten the craft exposed alot of that material, and to seal that with my 50/50 mix of alcohol & epoxy would take way too much to seal cause it would soak in like a sponge and defeat the purpose of cutting the holes.

So what I did was to mix up some 30min epoxy and used Q-tips to apply a thin amount of epoxy along all the cuts I made in the ply....When I'm ready to slap on the decks I'm going to seal the wood inside with my epoxy and alcohol mix, probably 3-4 coats, Until I get some shine from the wood, paying extra attention to the sponsons tips, under the sheers...

jetpack

My Feedback: (1)

A trick I learned a long time ago was to use cheap airosol hair spray such as final net and spray the wood pretty good with it like you were using it as spray paint. It weighs about nothing and drys to just about nothing, but what it does is form a barrier coat for when the epoxy goes on.

As the epoxy sets it dissolves the hair spray, slowing the absorption rate of the epoxy into the wood as your applying it. Less epoxy is needed to fill. It stays on top of the wood until you have your epoxy on and as it sets it is able to melt through the hair spray and grab the wood. Whatever epoxy does not make it past the hair spray it attaches itself to that. The hair spray already has some tooth into the wood fibers as it soaks in pretty good.

Do not overwork the areas that you are epoxying because this will loosen the hair spray and you'll loose the effect.

Believe It - Or Not.

Model airplane builders have been using this trick on balsa for years for when they glass.

Try and work the areas quickly to get your coat thickness, then move on to the next.

There's your seal coat.

As far as when I use straight epoxy or thinned depends on what type of wood grain I'm dealing with.

If the wood is solid such as the mahogany veneers in Dumas kits I would try and lay down one well-brushed coat for sealing but if it is hardwood plywood (birch) its better to use thinned epoxy because it goes straight through the first veneer and stops at the glue. It's good to soak that first veneer of the ply at least two thinned coats.

advanced builder

IF you read alot of feeds you learn something Will give it a shot hair spray. Your using top paint with KlassKote I like to use thinned pot. I use high lights to watch absorption. Razor blades during finishing. Where did you get the honing sticks ?

jetpack

My Feedback: (1)

You can find the sticks on this page at MSC industrial supply.

[link=http://metalworking.mscdirect.com/CGI/MWSRCH?N=30000179+4294171579+4294170950]MSC Industrial Supply - Polishing Sticks[/link]

R.J. West

hi Jetpack,
Iwent back and read alot of previous posts and stumbled upon one where you mentioned the same technique. The replies that followedbrought back some memories, wink..wink.

I gave Dumas a phone call today and asked about their wood, and also if they had any more Miller Americans or 1/8 Atlas's....No dice.. The girl told me that if theres any wood in the kit that you dont like, they'll replace it, free.....But the quaility is pretty much hit or miss, depends on what kit you got...which got me thinking, I didnt at the time, but I wonder if they'll stamp out a kit in 1/16 birch ply, if you request it?

The theory is sound, I like the idea however in my opinion, epoxy is thick enough to do the jobwithout"soaking in". When i say "soaking in" I'm refering to the type of soak you may experience if you attempt to seal those edges with thin CA....Thats a soaking....In the case of using something runny or that thin, then hairspray is the way to do it. I dont think its an issue in this case however...

Let me ask you something, If the epoxy sets on top of the wood, instead of soaking into it, what protection do you have if, for whatever reason, that wood becomes damaged or cut?

advanced builder

JP That site has some stuff could get lost in there for days.
Thank you Neil some of them sticks can get $$
I want some of the stuff where the girls are smooching all over you. does the hairspray have a smell like that??will that smell leak threw the epoxy so when I am on the water all the girls in bathing suits will come a running. I want it!

jetpack

My Feedback: (1)

[sm=teeth_smile.gif][sm=teeth_smile.gif] Just don't let the wife see all the empties. If she does, the boat excuse won't work.

advanced builder

I am not sure maybe the AXE commercial

R.J. West

Heres the latest updates on my pak 20

The hull is decked up and it feels light. I'm guessing around 1/2 lbs. I used a 1/8 ply doubler on the right sponson (inside the hull)and added 6-32 T-nuts for the turnfin mount. I cant believe that Dumas suggestes to use woodscrews.
I drilled out the holes for the T-nuts slightly larger and filled the hole with epoxy, after the epoxy has cured I redrilled the hole with the correct size drill bit and bolted the T-nut in, Just before it's in all the way, I put some epoxy around the base of the T-nut and tightend it down....by doing this I made sure that the hole itself is sealed. I have seen water damage on boats around screw holes in the hulls cause alot of modelers dont think about sealing them. water will seep in between the nut and wood...
I like this engine mount and will give it a shot. Its from here...http://www.solingerrc.com/index.html.

I used my iron trick to install the decks, by sprinkling a little water on the skin, and applying alittle presure and pulling upwards with my wifes iron & ironing boardI created a slight bend in the skin to flow along the curve of the frames....I then applied epoxy over each frame and a thin layer on the underside of the deck and taped her down. I set the hull upside down so that the epoxy will flow and pool under the deck instead of flowing down the frames.....

racer45

y

R.J. West

UPDATE!

I shaped the pine nose block & the two mahagony 1/2X1/2 blocks and epoxied those pieces in place. They are still in the rough. Work started on the cowl. The cowl itself isnt difficult, however it was time consuming mostly due to trying to get the best fit regarding the 3/8X1/16 stock thats used to make the small "ledge" that goes along the cowl's side. I had to make a mini sanding block from a formica sample. I used formica samples for years in hard to reach areas and for getting a good sharp edge. I get mine from Home Depot. I use some c/a and glue on some sandpaper on one side and trim around the edges..
I need to pick up some 1/8 ply stock as the 1/8 ply thats used for the "false floor", is cut too narrow. The false floor is the part of the deck that goes between the fins in the aft section.
Here are some pics of the pay n pak....And the real one....

R.J. West

Heres more pics that were sent to me.

In addition, I got my engine mounts from Joe Solinger and they look awesome! Unfortunately the mounting holes dont match up to my OPS .21. I havent emailed him yet, I was going to see if he would be able to make a new set if I send him my old ops .21 block as a template..Either that or find a .21 that will bolt up to the mounts, I dont want to drill extra holes in it.

jetpack

My Feedback: (1)

That's really nice to have that many photos to work with of the real boat.

I'm hoping to find lots of photos like that for my Atlas 40. I'm going to try and build that with lots of scale details. Finding crisp photos to know where the hatch plates are or rivet detail is hard to come by.

The Pay N Pak hull looks great with the full cowl, it's too bad it wasn't run more with it on. It could even work as a custom cab-over enclosed cockpit look if the back end was tapered off or left bobbed with a straight back pipe. I've been on the lookout for cowl ideas for my Eagle 40.