New Builder/First Air Boat
#101
Looks very good. I unfortunately did not fiberglass mine. Just a good sealing inside the hull, and a few good coats on the outside. I do not know how much of a difference in strength overall between glassing and non-glassing.
#102
Fiberglass helps keep the hull from flexing too much. It's well worth the hassle. I typically only glass seams and joints inside the hull (small scraps) and the bottom. I use resin only on the top - no cloth. It saves weight a bit and doesn't (hasn't so far anyway) sacrificed strength. Only do one layer of cloth. Just build up a couple 2-3 coats of resin on top of the cloth. 3 coats if you're thinning your resin (similar viscosity to polyurethane finish) or 2 coats if using a finishing resin straight up. On the bottom after final curing and ready for final assembly - sand the bottom with 240-400 grit sandpaper. It should help speed the boat up overall.
Last edited by 1QwkSport2.5r; 03-14-2017 at 12:18 AM.
#103
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Thats helpful to know. the main reason we ended glassing the top was to strengthen the joints, some of which were not perfect.
My next effort is the engine mount. Earlier it was suggested to make this movable to allow for CG adjustment. Would anyone have photos of how yours was built so i dont have to reinvent the wheel?
My next effort is the engine mount. Earlier it was suggested to make this movable to allow for CG adjustment. Would anyone have photos of how yours was built so i dont have to reinvent the wheel?
#104
Thats helpful to know. the main reason we ended glassing the top was to strengthen the joints, some of which were not perfect.
My next effort is the engine mount. Earlier it was suggested to make this movable to allow for CG adjustment. Would anyone have photos of how yours was built so i dont have to reinvent the wheel?
My next effort is the engine mount. Earlier it was suggested to make this movable to allow for CG adjustment. Would anyone have photos of how yours was built so i dont have to reinvent the wheel?
Look here: http://www.rcuniverse.com/forum/rc-a...0-90-size.html Post #8 you can see how I slotted the engine mount. Just an idea that works for me.
#106
I always set my thrust line (prop) to be parallel to the waters surface on plane - which most often is parallel to the keel/bottom for a flat bottom boat. I always play with the CG to get the boat to run true before messing with the pitch of the engine. A good starting point is having the bow hang at about a 20 degree angle lower than the transom when you hold the boat up by the tips of the prop.
#108
#110
Looks good. A couple cautions - if the aluminum angle you're using is 1/16" thick, it will crack. Also, with how far the engine is "hanging off" the engine mount, you may encounter lots of vibration and as such foamy fuel and a hard needle valve to hold onto. Ideally you want the engine to not overhang the edge of the pylons much if possible.
#111
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Thanks for the feedback-the aluminum appears to be 1/16" so I guess we will consider what to do there. For pylon/engine position it would be easy to slide the engine mount further back. With engine and boat we are at 5 lbs.
#112
Yeah, I would step the aluminum up to 1/8" which will add some weight, but I assure you it's worth it. My little .35 on my SI3 mini cracked the 1/16" aluminum within 6-7 tanks of fuel. If your prop is out of balance, it could happen sooner. I suggest being better safe than sorry.
5lbs is great. Hopefully it doesn't get too much heavier once fully rigged. A .40 will be good for reasonable performance up to about 6.5lbs. Above that, you might need to step it up to a .60.
#113
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So, we redid the angle with 1/8th. Nothing like doing something twice! Would you have any input on servo configurations? i was thinking to have them towards the front of the servo compartment as i fugured the cables need to flex due to the servo arm radial movement.
#118
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Oh dear...our last batch of epoxy is not drying well at all. its been a day and a half and still tacky! Any advice welcome. (guess poor mix ratio or not mixed long enough)
#119
You could try hitting it with a hair dryer or heat gun, but you will probably need to take a wetted rag (with methanol or acetone) and remove as much of the tacky epoxy as you can. Epoxy will not cure if you don't use enough hardener or mix it well enough. If it was mixed well and in the proper ratio, it may just be not warm enough. Generally, you want epoxy to cure at 70F or warmer. Try heating it good and see if that gets it to set up better.
By the way the boat looks good. Your air rudders may be too big, but it won't hurt to try it as it is.
#120
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Thanks, i picked up some acetone (heat made no difference. I read somewhere that rudders can be too small so i figured to shoot big and we can make smaller ones if needed (easily lifted off the pins)!
The boat has been quite a project! Never anticipated it to be so much work, but in a way its all custom so not surprising. If we make another that one will be a lot easier from what we learned on this one.
The boat has been quite a project! Never anticipated it to be so much work, but in a way its all custom so not surprising. If we make another that one will be a lot easier from what we learned on this one.
#123
Looking better and better. A couple of things from a newbie here. I built mine as per the plans and I do indeed need to increase the size of my rudders and was thinking of similar to what you have, as my turning was not the best in my opinion. Also, as per the suggestion, automotive paints will stick to epoxy, just make sure to 'rough' it up, but that goes for any surfaces to be painted with automotive paint. This also applies to most paints. By roughing up the surface, you will give the paint something to 'bite' into. Paint will also stick to non sanded and or shiny surfaces, but the adhesion will not be anywhere as good. Also, heed the advice of a good cleaning before paint.
#124
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Thanks. I noticed a few builds that had trouble with small rudders so we went big, and these should be easy to make smaller if need be as they just unhook. Years ago i build a speed boat and the local boat builder said rustoleum would be fine so thats what we used and it seemed fine. But I see many differing opinions out there on what to use on models. I do know a local auto body shop and perhaps he would be willing to airbrush primer and top coat.
amazing the amount of hours in this build!
amazing the amount of hours in this build!
#125
The only problem you could run into is whether the paint is chemically compatible with epoxy. Generally speaking, 2-component finishes are compatible with other 2-component paints. 2-component means the material uses a catalyst/crosslinker/hardener. There are limits to this however - polyester resin is 2-component, but will not adhere to epoxy and vice versa. I know for a fact that commercial 2-component waterborne polyurethane will stick to epoxy as does oil based polyurethane.. but epoxy won't stick to polyurethane. Some automotive paints are urethane based and others are lacquer based. I think it fair to say that a urethane paint will be a "slam dunk" whereas lacquer may not. You would need to do some test spots to determine adhesion before painting the whole thing. At minimum, use scotchbrite to break the sheen of the epoxy to aid adhesion. Better yet, use some 220-320 grit abrasive (sandpaper) to break the sheen. A quality finish/paint should adhere provided the substrate is adequately abraded. I may be making a mountain from a mole hill, but I'd hate for someone to have their paint peel.
As for the rudders - I haven't found a huge benefit from the height of the rudders as much as depth. Meaning a rudder that is wider (protrudes farther off the back of the boat) will provide more positive control than a narrower but taller rudder. If you read my thread about my SI3 flat bottom boat, you will see the "evolution" of my rudders on that boat starting with the rudders the plans outlined and the two revisions I made to improve steering control and response. Post #43 http://www.rcuniverse.com/forum/rc-a...-bottom-2.html
You don't expressly need to have your rudders' height match the height of the propwash. 1/2-2/3 of the propwash is totally good provided the width of the rudder is adequate. Do test your initial rudders first though - if it doesn't respond quickly or turn sharply, you will need to adjust the throw and/or the size of the rudders.
Besides building a strong hull, your rudders need to perform A-1 perfect. It's a real PITA if your boat don't turn for crap and she gets stuck in the weeds requiring going for a swim or canoe ride to recover it. I learned the hard way a time or two.
As for the rudders - I haven't found a huge benefit from the height of the rudders as much as depth. Meaning a rudder that is wider (protrudes farther off the back of the boat) will provide more positive control than a narrower but taller rudder. If you read my thread about my SI3 flat bottom boat, you will see the "evolution" of my rudders on that boat starting with the rudders the plans outlined and the two revisions I made to improve steering control and response. Post #43 http://www.rcuniverse.com/forum/rc-a...-bottom-2.html
You don't expressly need to have your rudders' height match the height of the propwash. 1/2-2/3 of the propwash is totally good provided the width of the rudder is adequate. Do test your initial rudders first though - if it doesn't respond quickly or turn sharply, you will need to adjust the throw and/or the size of the rudders.
Besides building a strong hull, your rudders need to perform A-1 perfect. It's a real PITA if your boat don't turn for crap and she gets stuck in the weeds requiring going for a swim or canoe ride to recover it. I learned the hard way a time or two.
Last edited by 1QwkSport2.5r; 03-26-2017 at 12:01 PM.