arcdude

I'm sure racers do get a lot more dings, I don't belong to a club or anything just doing this for fun otherwise my approach may be a little different. The tubes will be 1/2 tubes from the tub out to each sponson because I have no bolting mechanism for the center so the tubes will be exact to keep the spacing.

arcdude

Started to actually build the sponsons, what I'm doing is basically fiberglassing the inside and outside with 1oz cloth. I cut 2" strips and placed them around the perimeter and used 3 hr epoxy as this is compatible with all materials used and will allow plenty of time to get things properly lined up. The glue was put on the wood, primarily around the outside 1" and a line down the middle and thinned out around the edges so when it was weighted down glue wouldn't ooze out the sides. I babysat things for quite a while and still found a couple of spots where glue had come out the sides so I smoothed them out as it set up so when I install the remaining panels there won't be any lumps or bumps. I expect the combined weight for the two sponsons to be around 1 pound when completed.

Jeremy_H

I don't recall seeing that method anywhere before, interesting.

arcdude

I don't recall seeing anyone else doing it quite this way either, it's a method I adopted to models many years ago derived from my full scale boat building experience, similar to stitch and glue method of building strong butt joints. The end result is minimal glue and an incredibly strong joint being glassed inside and out. I've never shared this method by the way so if it assists someone in there process that'll make me happy, we all have our little tricks

arcdude

I managed to get both sides on each sponson glued in place and decided to add a couple of blind nuts on the right hand sponson in the event I decide to add a turn fin at a later date. All sponson tubes lined up perfectly which is a relief, I was a little concerned gluing the parts without them installed. Now that the sides are glued the rest of the panels should go quite quickly as there is little to line up.

Jeremy_H

Good idea on the turn fin. I've not used one properly yet, looking forward to fiddling with those.

Jeremy_H

By the way why did you choose the right sponson for the turn fin?

arcdude

There are a couple of reasons for that choice, one being the rotation of the prop as it will turn right easier than it will turn left as with flying an airplane and you do a knife edge (flying on it's side) it will go to the left easier as the prop is pulling the front of the plane upward. Secondly I'm right handed and going in a clockwise rotation seems natural, not much of I reason I know. And the last and least important, it seems that is the way most boats are set up.

Jeremy_H

OK, here's my perspective. If we agree that there's a difference between right and left turn due to the engine direction of rotation, then that would be due to a reactive force from the engine's rotating mass, and through a reactive force from the resistance against the propeller. We call this torque effect, which is partially correct. RC boat engines came second in the ranks of model engine use, and as they were converted aero engines suddenly we had model boats with engines that defied the conventional direction of rotating, through being mounted backwards. So full size boats have propellers that rotate clockwise when you are facing forward, that is a 'Right Hand' propeller, so by definition, and against popular thought, the model boat engines are running left handed propellers (you'll find that the modelling fraternity actually call these right hand, go figure. It's because 'right hand' is associated with 'normal'). As a consequence, to maximise turning ability full size hydroplanes are fighting against a force that is trying to rotate the boat anti-clockwise when looking forward, so to use that they make left turns around the course. Model boats, as the engines are actually going backwards against the convention of full size boats, they make right turns on a course. With our aero engines facing the 'correct' way, the opposite applies. As such the most effective turns are to the left, so the turn fin should be on the left, or port, side with its function being to hook the inside of the turn.

This issue has bugged me for years, and it's one of the primary reasons for my building an in-line twin as it removes the difference, but if you check around you'll find that airboat hydros are mostly rigged for left hand turns, it'll only be the other way with a pusher engine.

I'm not sure where your aeroplane analogy sits to be honest, aeroplanes have a tendency to roll left for the same reasons as an airboat, reacting against the direction of rotation, as such a plane will flick into a roll left easily and with a bit of elevator your turn is there with some rudder to keep the nose up, going right needs more aileron. Rudder turns in a plane will be flatter right than left. But I'm not sure what the 'easy' bit means, it can be 'easier' to control a right turn because it reacts less, which is different to the plane's ease of getting into a maneuver.

Current evidence. Every SI3 hydroplane turns left on speed runs, every SI3 with a turn fin has them on the port side. My narrow built 'Miss FivePoint' has been setup so that I can turn the boat at full speed in either direction without the boat flipping, this was done by trial and error, the resulting turning circle to the right is three times the radius of the left turn.

It's interesting that you feel that right handedness means that right turns sit well with you. If I can use a tennis analogy to me it feels that right turns are backhand, and left right are forehand. I think there's a reason for that. I recall when I was younger that when I thought about my boats they'd be going right to left in front of me, a forehand pass, now I'm older I've become so conscious of keeping a distant boat in order that I picture them far away going in the same right to left direction, but now it's the other side of the course!

1QwkSport2.5r

If you have an engine that can be made to turn clockwise, using a pusher prop will allow you to run the engine clockwise and still use a tractor setup if you indeed want to turn right. I have several engines that I can run clockwise (my ST S90 is one of them) but the availability of pusher props is limited so I stick with normal props and turn left.

Build looks good so far; I need to get on my computer to get a better look at the photos. A smartphone screen isn't big enough to do any justice.

arcdude

Umm, not sure what happened there, Brain fart maybe, not sure if I can say that? Yes Jeremy you are absolutely correct. Not sure what I was thinking but yes it's a little thing called to every action there is an equal reaction hence go left, the other left. At the last minute I decided to make provisions for the turn fin and never having seen an airboat with one I sort of just visualized the rotation of the prop and forgot all about the equal reaction, simple as that. I'm getting older I have no legitimate defense at this point in time! On the plus side thankfully it's not too late to install blind nuts on the other left sponson because I haven't glued on the top sheeting yet. Thank you, but be a little quicker about it next time will ya. And I still want to turn right, I recently purchased new radio, the pistol grip type so it may take some getting use to, especially going left

Jeremy_H

Haha!, brilliantly fenced response sir

arcdude

Thanks for the tips on the props, unfortunately it was a monumental blunder on my part as explained to Jeremy. The build is now getting to a point when it actually starts to look like something other than a pile of lumber so I'm definitely looking forward to seeing how it turns out.

1QwkSport2.5r

I will add that the SI3's do turn right quite well, you just need to slow down a little more and ensure the servo and rudder have enough throw. As to turning with an outrigger - longer boom tubes will aid in turning. Shorter booms are better for speed runs but of course there at the expense of stability. I'll get on my computer later and check out your latest photos.

Jeremy_H

If you want to turn right and have a turn fin I'll let you know how I get on with an idea I have.

arcdude

look forward to hearing what you propose to do.

arcdude

Now the sponsons are pretty much built and blind nuts installed into the left sponson as well so at least all doors are open for experimentation. I figured this may be a good time to check the weight of things to see if I'm on track and as can be seen on the scale it states 7.10 oz or 202 grams at this point, the nose still has to go on and fiber glass the whole sponson so that will add a couple of oz's to overall weight. My goal was to be at about 1 lb for the two sponsons so I won't be too far off the expected weight in the end, not too bad.

Jeremy_H

Nice quality work Arc

arcdude

Thanks Jeremy for the kind words. At the present I'm somewhat in a bit of a stall, I can't seem to decide on motor mounting and due to the fact the body is foam and requiring reinforcements for the mount I can't proceed until a decision is made. I have only seen two different mounts so far on similar boats so not a lot of reference to draw from. I would like at least 2" forward and reverse adjustment in the mount as well as 1" up and down to accommodate different props. The adjustment part isn't where I'm challenged but rather the upright supports to the mount. Everything I've considered I always come back to a single post arched to the front, which is what I'd prefer in the end however strength and vibration seem to be getting in the road. Should anyone have any suggestions I'd be most appreciative in hearing them, Thanks,

Jeremy_H

If it were me, being a development boat, I'd get over that progress barrier by putting rails on. That would allow the tub to be built. Then the pylon design can follow, the only gray area in this is ball parking where the rail should be.

An alternative might be to build in tapping plates. Right now I'm thinking angle aluminium, say 25 x 50 or 1" x 2", nestled on the inside faces of the deck (the 25mm section) and the tub sides (the 50mm bit). Lighten the 50mm section with holesaws or something. This would give a plate towards the side of the deck to drill and tap into later, with large load spreading webs down the tub sides. I'll draw it if that's not clear.

arcdude

Agreed on the development part for sure, that is why I have pretty much given up on the pylon idea at least for now. Here is the idea I've come up with and if you could offer your thoughts it would be great. I have been looking at the SI3 engine mounting frame and what could be simpler than that and it provides an engine mount and fuel tank holder at the same time. So what I have been considering is that type of mount and to mount it to the tub by installing 1/4" aircraft ply under the deck (about 6" long and side to side) on the top and bottom of the tub and drill down through the whole thing and install wood dowels to connect the top to the bottom and at the same time the plates would also be connected to the sides when they are glued on. The main concern I have with this is I want the battery compartment directly aft of the back of the engine, my goal is to have the C of G an inch or two behind the trailing edge of the front sponson's. I believe I understand your idea, I do have the aluminum and just haven't come up with a very good idea on how to use it. If it wouldn't be too much trouble I would appreciate you drawing it up before I make a decision on which direction to go. Thank you

Jeremy_H

Left image is a cross section of the tub, bulkheads would strengthen it. right pic is just a side view of the ally with lightening holes.

So you see nothing outside of the tub, just drill through the ply deck and the ally and tap a thread into it to bolt down whatever you want.

arcdude

Thanks for the input Jeremy, appreciate the thought. There is a couple of issues that arise with the aluminum installed in that manner, the top has an arc to it and the lite ply isn't the best material to really snug a motor mount down to with a solid backing behind it and I would prefer a more solid footing for piece of mind. Another good idea would be to deflect some of the motor mount stress's through to the bottom of the tub as well. Guess I'll just have to ponder this a while, Cheers.

Jeremy_H

Still pondering?

What about just having the tub sides come up above deck level to provide vertical rails each side. Again fixings would be going through the ply, so perhaps just cheek the lite ply with some Birch ply and bring that above the deck. Cheek it with aluminium even.

arcdude

As a matter of fact yes I was and still am pondering. Thanks for joining in on the whole pondering thing, appreciated. The idea of ply up the sides was and still is a consideration, kind of leaving tabs sticking up that the mount can be bolted to. As much as I'd like the quick route to get going I can be a tad fussy in the outcome and would like something that will be pleasing and functional in the end (it can be a pain sometimes not being able to settle). I am leaning towards something possibly on the upper and lower deck tied together somehow so the motor stress's are distributed as much as feasible. The consideration is to inlay a piece of 1/8" aircraft ply under and through the top layer of lite ply and a further recess towards the center for the radio box and when complete the entire finish would be flush on top and provide blind nut locations through the aircraft ply in four places for the engine mount. That way the load is distributed throughout and solid bolting for the mount without crushing any of the finish. Not sure if you know what I'm getting at or not, actually I'll do a little doodle in paint so it'll be a little clearer.