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Aug 30, 2019, 03:09 PM
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Fibreglass boats from scratch


Hello there! I wanted to create this new thread, since i wanted to share my progression with the fiberglass boat i started building 3 years ago. I only finished the bottom part od the hull, and put filler on it *bruh. I trashed the project since i didnt know too much about building then, but our holiday at the mediterrainean inspired me to finish that boat. So i roughly made the upper half of the hull, no filler this time. The hull molds were made from plaster that i put over a model od that boat i made from depron. I didnt refer to any real boats or anything, and so i have a hull thats as tall as a skyscraper and has a deadrise of about 35°... I dont care if its not good, but im very curious about the performance. I plán putting an overpowered brushless system in there.

So what do you think, will she sail? Im open to any suggestions, critics, opinions

I hope the read wasnt too boring, and if your interested, stay tuned! I will keep you updated!
Last edited by Jansvast; Apr 03, 2020 at 11:06 AM.
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Aug 30, 2019, 03:57 PM
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looks good. whats the length and width of this hull ? also whats the degrees of the hull - v ?
Aug 30, 2019, 04:14 PM
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The "degrees of the hull" is called deadrise i believe, and its about 35°. I know its too much. Lenght 44 cm, width 13 cm. And also i will cut the top part lower, so that its not sticking out to the sky like that . I made the bottom part when i was 12...
Last edited by Jansvast; Feb 25, 2020 at 12:34 PM.
Aug 30, 2019, 10:38 PM
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Don,t think you need to cut the sides down lower as its doesn,t look to bad as is with the deck sitting on. keep up the good work and for motor power i would be looking at running a 2s battery pack power and a suitable motor and esc etc.
Aug 31, 2019, 12:46 AM
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With that steep of a hull, it will be nice in choppy water i hope. I was hoping to install a quick 3-4s system. Today i will cut the sides clean and maybe join the two halves, but im not sure if i should install the motor mount first.
Last edited by Jansvast; Aug 31, 2019 at 12:47 AM. Reason: Spelling
Aug 31, 2019, 02:01 AM
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I don,t think your size hull would be suited to 3 / 4s power due to its overall size. you can get very good speeds from a 2s set up.
Aug 31, 2019, 03:23 AM
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Oh yeah! Thats much more like it! I cut the top part clean, also lowered the sides too. It now looks much more like a speed boat
Aug 31, 2019, 04:27 AM
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Hi Jan,

You're going to need a lot of weight to get the boat to run stable and stay upright, the angle of the bottom should have been made to get more shallow towards the rear to provide stability.

I made a similar hull years ago, I still have the mold, see the pictures here: https://www.rcgroups.com/forums/show...3&postcount=25

The angle of the hull runs from 45° at the nose to 15° at the transom.

Regards, Jan.
Aug 31, 2019, 05:08 AM
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Hello, pompebled! Im glad youve taken a look. I just tested her in the tub, shampooo bottle inside adds weight. I dont know, however, if should i close the hull today and add the motor mount and drill holes later, or if i should do it now and glue the halves together later. Im also unsure about the motor position. Should i put it in the front and the batt. behind it, or the other way around? I imagine the cg shoud be pretty far back.

PS: i had no idea what i was doing when i was 12. I just found it in the wardrobe and decidet to finish it now, 3 years later If it doesnt run well it doesnt matter too much, but i will try my best.
Last edited by Jansvast; Aug 31, 2019 at 05:11 AM. Reason: Forgot pictures
Aug 31, 2019, 06:31 AM
Boaters are nice people.
Hi Jan,

The CoG on a fast electric should be between 28 and 32% of the hull, measured from the transom forward.
Floating in the tub it doesn't look bad at all, but keep in mind that when she moves through the water, the hull will rise up and you'll have a lot less hull in the water, the steep angle may cause an unexpected running attitude where it falls onto one side when running.

Make sure the hull is watertight, so it won't fill up and sink on it's maiden trip.

Do you have some measurements, length, width (beam) and weight?
We may have some suggestions on what to power it with.

Regards, Jan.
Aug 31, 2019, 07:01 AM
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I sure have. Its 44 cm long, beam is 12,7 cm. Should i mount steps to the hull? Or do you think it will work without them? I plan testing it with only rudder first, and then put steps, trim tabs and fins on if needed. I made the fins and tabs out if 1 mm aluminium sheet. The metal thing on the rudder is a geometry improvement that moves the pushrod mounting point straight to the hinge line. Some pics:
Aug 31, 2019, 07:33 AM
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The hull including trim tabs, fins and rudder (no screws) weighs about 250g, but i still need to join the halves together so she will get a bit chunkier after that . My budget is rather cheap tho...

Edit: would you drill the holes and glass in a motor mount before or after joining the halves?

Jan
Last edited by Jansvast; Aug 31, 2019 at 07:53 AM.
Aug 31, 2019, 08:50 AM
Boaters are nice people.
Hi Jan,

Our boats have a canopy/hatch that closes the hull and is secured with tape around the edges, so the bottom and top half are laminated together.
This also prevents the hull from warping when building in a motormount and the propshaft.

Steps ( 90° to the keel line) is something you can't add to an existing hull without radically changing it, if you mean strakes, that's possible, I would at leas add a triangular strip along the edge between bottom and sides to prevent the bowwave from crawling up to the deck.

I would power a 44 cm hull with 2S and a watercooled inrunner, something like this:
https://hobbyking.com/en_us/2848sl-3...tercooled.html
On 2S you'll have about 26000 rpm under load.

You can also use an outrunner like this, but that would have to be mounted on a watercooled mount to avoid overheating:
https://www.banggood.com/Racerstar-K...r_warehouse=CN

Regards, Jan.
Aug 31, 2019, 09:16 AM
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Thanks for awesome information, how fast could a setup like that possibly go? It is too expensive for me tho, so i would use a cheaper equivalent. I will use a regular plywood motor mount.

I assume i dont need a strut on such a boat, and i will try to get the prop angle as close to neutral as possible, and the motor would sit very close to the keel. I would like to run 3s, so a bit lower kv would maybe suit well. I aim for a speed of 50 kmh or more if possible.

Yes i misunderstood what steps are

The thing im the most curious about is the motor/battery placement. I imagine the motor would be more in the front and battery behind it so i could move it to adjust the cg.

Regards, Jan
Aug 31, 2019, 03:35 PM
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With a setup like this the boat balances st about 29% (3s 2200 mah, and a similiar motor)


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