CalvaryCustoms

Let me first applogise, I know this is the aircraft forum, but there is no composite forum in the boat section... I have a 1/5 scale unlimited hydroplane that is 72" long (build from enlarged 45" plans). She is mostly 1/8" ply ribs and sheeting, with balsa blocks shaped to make the fork tips, and 1/8" balsa ribs and sheeting making up the rudders and "stab". the small "braces" inbetween the forks are also 1/8" balsa ribs and sheeting. The spars running lengthwise between the ribs are 1/4 x 1/2 balsa. All of the exterior sheeting is 1/8" ply.

Shes not finished yet, but I just thinking ahead here. I had originally planed on taking the finished hull to a marina or auto body and have them do the fiberglass for me. After getting a couple quotes... I've decided to do it myself.

I have never done fiberglass before so I am totally new to this. I have read up on everything I can get my hands on fiberglass layup, but i still have a fue questions...


1. Weight is less of an issue than with planes, but it is still a concern. I want a solid skin, but i don't want to add 50# to the hull eather. I have seen cloth from 3/4 oz. up to 50 oz... but no one says what to use on what kind of project... I'm thinking a layer or 2 of 2.3 oz cloth aginst the hull with a 3/4 oz top layer for a smooth finish... The engine compartment I'm thinking 3-4 layers of 2.3 oz... How far off am I ?

2. With the complicated angles of a hydroplane, I think the cloth will need to be cut in areas to form around some edges. Will the overlap be noticable in the finish ? If so, how can this be smoothed out.

3. Can you add cloth "tape" or formed strips in high stress areas with out having bumps or bulges in the finish ?

4. When the fiberglass is complete, can it be gelcoated ? Everything I've read talks about gelcoating the mold, then doing the layup.

5. I've seen planes with no sheeting at all fiberglassed like you would monokote them. How is this done with out having resin inside the wing, or the fiberglass or wing itself warping during cure ? My buddy wants me to build him a copy of the hull when i'm finished. Can this "skeleton fiberglass" be done w/o any sheeting on a hydro ?


I have added a fue pics of the Hydro, hopefully this will help.

Thanks in advance for any insite, suggestions, opinions, or comments.

seanreit

My Feedback: (60)

Call me at 512. 656. 2357 and have a pen and paper ready to go.

You will get a lot of advice here, and I would encourage you to compare my notes with what you learn in this thread, and then make a best decision for yourself.

I will be available anytime after 8am central tomorrow morning.

dreadnaut

My Feedback: (5)

I would layup at least 6-8 oz on the bottom. Go for half that on top. Curves will be a problem, be patient and do not cut the peices more than about 1/2'' oversize, or it will be hard to work with.

seanreit

My Feedback: (60)

Dread, I had a pretty extensive conversation with the guy today, I had recommended 2ounce or so. Any particular reason you are suggesting 6 to 8 ounce? I have laid up a lot of 8 ounce glass on Fiberglass fuse's, and I would personally consider that a whole lot of extra weight, but not sure the benefit you are getting there? Is it for durability? My thoughts were that the strength of the model would be in the build, and then you simply want to protect and seal the boat.

I know opinions are just that, but I have never built a boat, and showed him several examples, pictures, and instructional material, and ultimately he will have to make a decision so I thought I would add in the mix what I told him so it's layed out and not TOO muddy.

Thanks in advance.

There is a 6 ounce loose weave out there that I have used, that might not be a bad choice, but the 8 ounce heavy weave I used make a 5lb fuse with two layers on what I have been able to get in at 3lbs using other methods, and 1 lb using honeycomb.

dreadnaut

My Feedback: (5)

I admit, I have never done a boat, but I know that water is a lot ''harder'' than air. In choppy water, at high speed, there will be a lot of impact.

CalvaryCustoms

Dreadnaut, You are right. With aircraft, you renforce areas that will fail first due to G's. Boats are no different, you renforce the areas that will come in contact with the water the most. With a Vhull (skiboat or scrab), it is the Keel, or very bottom of the V. A Catamaran is the bottom of the the sponsons on both sides. A Hydro is the bottom of the forks in the front and the back of the sponcens in the rear. The picure below shows the high stress areas that will take the most abuse in red, with a little less stress in the blue areas.

I'm actually leaning toward Carbon Fiber renforcement in these areas due to the added strength propertys.

Just as with a plane, a boat needs to be "trimed out". The trick with a boat is to get most of it out of the water. The smaller area in contact with the waters surface, the less drag, and the faster it will go. A hydroplane is a very unique creacher, it is a lifting body. They are designed to let air under the hull so the main body (the flat areas on both sides of the cockpit) actually act as a wing to lift the boat out of the water at high speed.

Due to this "Flying" idea, you want a hull that is very rigid with no flexing from tork, or while bouncing around on the water. If the hull flexes and disrupts the airflow under the boat, it will be very unstable and hard to control... Kind of like flying a plane at stall speed.

I hope this helps, and thats for all the help.
Tim

Justaddwata

My Feedback: (3)

Stresses on the red areas are not going to be as high as those in areas where you will realistically see loads applied. The side sponson where the turn fin is mounted will see probably the most of the whole boat. Also where the sponsons attach to the hull. Also dependong on what you are using for motor support additional support on that big flat hull where the cmounts will be, the cable will exit and the transom where the drive and notably the rudder are to attach will all see their share. Also if you want the hull to survive a flip you want to strengthen all you want to survive a water impact. While this adds weight - you can afford a little more than the plane guys will consider.

planebuilder66

My Feedback: (8)

I know this thread is old but the density of water is 800 time that of air, so with that said, 2 oz cloth for the bottom is good but a final coat of .75 to 1 oz cloth over everything including the bottom is a good solid foundation for years of abuse. I like to use west or MAS epoxy resin, think twice before using polyester resin, the cure time is too fast and chances for dryspots or wrinkles is too common. One can of west system has lasted me about 2 years for glassing various planes, for a average small plane it adds about .5 to 1 oz of weight using just .75 glass cloth, for a large aircraft (1/4 scale) it adds about 3 to 6 ozs, but thats using 2 ozs cloth.

c-cat

Might have been a good idea to glass all internal's in sheet form before building. Even the sheeting (inside) could have been laminated prior to building. I'm really surprised many don't do this on their max-cat or v builds. Balsa in sheet form tends to absorb a ton of resin which means wetting out the wood before glassing can begin. Otherwise balsa will draw resin from fiberglass making it useless. I would consider first sealing with resin. Then perhaps some carbon veil in general areas inside, along with a medium weave twill for running surfaces. The twill drapes and conforms real easy while building glass weight and strength like traditional glass.

Bill Diedrich

Balsa not only will absorb resin, if not sealed will absorb water also, causing
premature failure of the internal structual parts. I ran model boats for 20 years
before getting back into aircraft and have used all types of materials to build
boats with, except balsa because of it's sponge like chacteristics. For the size
of the boat being built, it was not a wise choice of material to plank the boat with.
Okoume plywood would have been a better choice of wood, it is light and very
flexible and more importantly marine grade ply. It also has the strength of aircraft
grade ply, but is more flexible.