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Old Jul 07, 2013, 06:15 PM
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Goat Island Skiff build

Hey guys,
My uncle has just built the full scale version of this boat from plans:
http://www.storerboatplans.com/GIS/GISplan.html
And I would rather like to make a 1/6th or 1/8th (depending on storage, sail size etc) version of it to sail as radio control.

I'm no beginner to building from plans/scratch and have many aircraft and a couple of other boats under my belt, but in those cases they've always been intended for rc in the first place, so materials and thicknesses are all appropriate etc

So my first question is, what thickness/type of wood should I go for? Would a ply frame with balsa skins be sufficient?

Second question is, what control mechanism would I need to use? is it just a case of rudder and a winch or strong servo to move the sail from one side to the other? (I have never sailed an rc boat and have only very little experience with real sailing)

Third question is, would I need to add a keel of some sort?

and lastly, how frowned upon would it be to put some sort of small motor and prop in it (concealed somewhere under a seat/ 'luggage' etc) for if (when ) I get stuck?

Sorry for all the questions, and thankyou in advance
Looking forward to this build!
James
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Old Jul 07, 2013, 09:36 PM
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United States, CA, Riverside
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James,
You will get a lot if differing opinions, but here are mine.
Balsa would be fine, 1/16" if covered in fiberglass. I would probably build it in 1/16" ply.
Rudder and winch is all you need. At 1/6 scale the sails will be about 400 sq. in. if I am doing my math right. Futaba and HiTec both have good, inexpensive sail servos that wold work fine.
Yes you will need a keel. Look at the RG65 sites for ideas, I would think something along those lines would work fine.
Last, it is your boat. A motor will add a lot of complexity, speed control, etc, but if you want to do it, do it. Don't worry about what others think. In my experience, it will not be needed. Sailboats don't really get stuck that often. If the wind dies, just wait for it to pick up, or for the current to push your boat to shore. This just provides good time to visit with the others at the lake you are sailing at.
Have fun,
Brad-
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Old Jul 08, 2013, 02:37 AM
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Quote:
Originally Posted by -james- View Post
..... Second question is, what control mechanism would I need to use? is it just a case of rudder and a winch or strong servo to move the sail from one side to the other? (I have never sailed an rc boat and have only very little experience with real sailing)

Third question is, would I need to add a keel of some sort?

and lastly, how frowned upon would it be to put some sort of small motor and prop in it (concealed somewhere under a seat/ 'luggage' etc) for if (when ) I get stuck?
... James
Cannot help re construction material...

Re control gear - a simple servo for rudder, a sailwinch for the sail
Something like this one perhaps - depending on the scale you build:
http://hobbyking.com/hobbyking/store...60deg_55g.html

Re a keel - I would think you will need to add a drop keel (a lead bulb on a fin) - dimensions to be considered

A motor - I totally agree with Nikram - a motor is unnecessary, just adds complication and unnecessary weight. Also, it takes a serious motor to overpower even a small sail.

Hope this helps
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Old Jul 08, 2013, 05:04 AM
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Hi guys
Thankyou for the replies, looks like i'll forget about the motor, if worst comes to worst i'll get my tug out and give it a good push back to shore

Thinking about it, 1/6th may be a bit big for me to store, is 1/12th (approximately 40cm/16 inches) too small to be practically usable?
However I hope at that size I wouldn't have to fibreglass anything, as that is cost and complication i'd rather not add having never done it before
Thanks again,
James
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Old Jul 08, 2013, 12:11 PM
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I think at 1/8 scale, it would be about 24", a nice size. Using balsa as the hull material will need fiberglass, but thin ply you would not. Both will need to be sealed well. Fiberglassing is not that hard, but it does cost a few $$. A 16" boat wold also be fine, and there is a class called Footies at just 12", fun little boats. The larger the boat, the better it will pass through rough water.
Brad-
Quote:
Originally Posted by -james- View Post
Hi guys
Thankyou for the replies, looks like i'll forget about the motor, if worst comes to worst i'll get my tug out and give it a good push back to shore

Thinking about it, 1/6th may be a bit big for me to store, is 1/12th (approximately 40cm/16 inches) too small to be practically usable?
However I hope at that size I wouldn't have to fibreglass anything, as that is cost and complication i'd rather not add having never done it before
Thanks again,
James
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Old Jul 08, 2013, 04:12 PM
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Would dope and tissue on a 16" model be an ok alternative to fibreglass? I have that stuff lying around from free flight aircraft i've built in the past
The 32" version is definitely a no go, wayyy too big after thinking about it, 24" could be ok but atm it's looking like 16" is the way forward. I guess I can always build a bigger one later on if I find that it's too small to sail and (depending on the finish) give it to my uncle as a static model for his house.
James
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Old Jul 08, 2013, 11:49 PM
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Never tried dope and tissue myself, anyone out there try it?
At 16" you won't need a sail servo, just a good standard servo will do. You will need to figure out a way to keep it from swamping. I have seen people use thin plexi to keep out the water from the open hull.
Quote:
Originally Posted by -james- View Post
Would dope and tissue on a 16" model be an ok alternative to fibreglass? I have that stuff lying around from free flight aircraft i've built in the past
The 32" version is definitely a no go, wayyy too big after thinking about it, 24" could be ok but atm it's looking like 16" is the way forward. I guess I can always build a bigger one later on if I find that it's too small to sail and (depending on the finish) give it to my uncle as a static model for his house.
James
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Old Jul 09, 2013, 05:49 PM
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Dope and tissue will work well on a small model. Not adding much strength, like fiberglass would, but waterproofing and smoothing the wood for a nice paint finish. You'd probably be better off using thin plywood, like 1/32" or even 1/64". Thin plywood like that is stronger than balsa when curved into a hull, but can be cut with scissors.
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Old Jul 09, 2013, 06:03 PM
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@Mark:

Further to the discussion on size of the finished boat...

For what it is worth, smaller sailboats are quite a bit harder to sail than slightly larger ones, also they are only suited to very light wind.

My smallest sailboat is 500mm and is a real handful in anything but very light conditions, blowing flat in slight gusts. My next smallest is 800mm and that sails well in most weather.

*****IMPORTANT*****
One other item for consideration relating to scale - I am thinking you are planning to build from the original (full size boat) plans. As you may be aware, there are some issues when scaling down for working models - while length reduces by scale directly, area reduces by scale squared and volume reduces by scale cubed.

With this in mind:
1) the scaled down sail area will be very small in comparison to the hull size - not really a problem except the boat then has little power.
2) the scaled down displacement (hull volume) will be greatly reduced. This will mean reduced buoyancy, so that the weight of the boat will become a serious issue.

It is these factors that lead to the non-scale keel fins on model sailboats - the Footy for example has a keel fin that is nearly the length of the hull. This long fin is needed to get enough leverage without too much weight to counteract the sail loading.
(Hope this makes sense.)

As it is an open boat, you would need to plan for the boat being blown flat and filling with water. I saw a mention of clear plexiglass over the cockpit somewhere I think?

Re the sail servo - in a 500mm boat a standard servo with an arm on it will do the job as long as you have room to swing the arm in the boat. You may need to use double haul to get enough sheet travel, but that is no big deal.
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Old Jul 10, 2013, 07:54 AM
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Thanks MrPenguin, that does all make a lot of sense, seeing these complications of a small sailing boat, i'm thinking of having the sail folded up and just powering it with a small ~200 size motor and 2s 500mAh lipo.
I'm up to the point of installing radio gear pretty much (I've been off the past few days and have worked pretty much non-stop ) and i'll post pictures later and see what you all think about installing some sort of propulsion system (be it sail power or motor )
Regards,
James
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Old Jul 10, 2013, 01:00 PM
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Here you go, progress up to now
Full length shot


This is where I would place either the battery for an electrically powered version, or the standard size servo to move the sail


Thoughts for the rudder is a pull-pull system on the tiller with the servo concealed under the deck.



Detailed picture of the rudder, still to be sealed and finished etc, only shown slotted into place dry


Regards,
James
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Old Jul 10, 2013, 06:51 PM
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Quote:
Originally Posted by -james- View Post
Thanks MrPenguin, that does all make a lot of sense, seeing these complications of a small sailing boat, i'm thinking of having the sail folded up and just powering it with a small ~200 size motor and 2s 500mAh lipo.
I'm up to the point of installing radio gear pretty much (I've been off the past few days and have worked pretty much non-stop ) and i'll post pictures later and see what you all think about installing some sort of propulsion system (be it sail power or motor )
Regards,
James
@James:

She is looking lovely, great work so far!!!

Even if you leave the sail furled and use electric power, I would think you may need some keel to balance the mast and the wind loading you will get above deck.

For a small boat like this I would think a single link to the rudder should be adequate as the loading is quite light. I use single link on a one metre boat, no issues. And if the rudder servo is close to the transom shaft flex will not be a problem.

Re the propulsion - well it IS a sailboat, so I would vote for sail power if you are looking for votes.... However, it is YOU that is building and sailing her and the decision rests with you....

Sail power is probably simpler to do. You WILL need a drop keel and maybe consider enclosing the deck with clear material. With electric propulsion, you need a tube, prop shaft, somewhere for the motor, far more battery capacity and the need to squeeze more electronics in.

You may get some inspiration from the following thread of the build of a novel Pram Dinghy being sailed by Kermit the Frog. The last photo on page 5 gives the only view of the keel, and that is distorted by water.
http://www.rcgroups.com/forums/showthread.php?t=1275629
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Old Jul 11, 2013, 03:43 PM
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Thankyou for all your help MrPenguin

Today I built the sail, rather crude but I have no access to better materials than shopping bags at the moment



The sail hinges at both points where it attaches to the mast, with a movement of ~80% either way

My question is now, where do I place a servo for the sail etc? and furthermore, how do I connect it? I haven't really got access to an LHS as it's only open fridays and saturdays and i'm unfortunately busy for both those days this week, so with that in mind if I can do it with parts I have lying around then that would be great

EDIT: Oh and here's the rudder linkage, two ball clevises simply linked together, the servo stands vertically to minimise space usage
Please excuse the card mock-up of the rear seat




Cheers,
James
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Old Jul 14, 2013, 11:12 AM
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Great looking model and nice build thread too! I've been very happy with my one-channel pram dinghy. Simple and fun. You will appreciate every minute you've spent when its on the water.

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Old Jul 14, 2013, 06:40 PM
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Well it sails!!! Had it's maiden voyage yesterday with the naff carrier bag sail shown earlier, but I spent an hour or so with my mum tonight sewing up a new one out of some cotton, looks much more scale!
The maiden went well, I managed to get it back to where I was standing which is always a plus!
Here's some photos of the finished model, and a video link will be added later on









Hope you all like it!
A big thankyou to everyone who has helped me out in this thread!
Regards,
James
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