Infusion Plan

Diab publish a sandwich handbook. If you're technically oriented it gives you all the equations to design sandwichs. Ham and cheese, carbon and foam, beef and pickle ect. Peter

 

I was just trying to understand the part where you said the core must be flexible to gain strength in a sandwhich system. Now I understand, the core must be more flexible than the laminates strength to gain any strength.

Im not too worried about the coosa as the mfg told me I have to laminate both sides and there is lots of people using it with motors 3x4 times bigger.

Thanks for that explanation. The 1/4 inch corecell is much cheaper than the 5/8, I have to check on wood, I think you might be right on cost being more there. So now I understand on asymetrical stress, I think.

 

Theres 2 very different things to consider when looking at all these problems, and the main difference is the TYPE OF LOAD your dealing with. Peter, youve only talked about bending loads. The other main type of load you need to deal with in your boat Jorge, is localised compressive loads. This is why youve used coosa board in the transom, for its much higher compressive strength. An outboard bouncing around on your transom skipping across waves its actually a very complex 3D load situation with a combination of compressive, bending, tortional and more all occuring together dynamically and transferring the loads at very acute locations of the bolts, and outboard bracket edges.

I was also thinking about your hull bottom, you probably should have used corecell M100-130 to provide more compressive strength for high speed wave impacts - i know your in flat water most of the time, but im sure there will be a time when you need to cross s bumpy stretch of water... alot of builders use balsa cores on the bottom for this reason (and not pay the premium for higher density foam).

back to the first problem of your transom laminate, because the loadings are so complex, its a bit of a black art and a very difficult engineering problem - even for a professional. Most professionals would simply apply a massive safety factor to make sure it didnt fail rather than do a complex analysis for such a small job. The extra materials would cost less than the engineering fee, so why bother... What you can do (and its what im doing) is to ask successful race boat builders what theyre using... Theyve achieved close to the minimum laminates by trial and error, if it broke, make it stronger... if it didnt broke, make it lighter etc...

Thing is, you need to find someone with a similar size/shape transom which it could be compared to, and this will not be easy.... if you have plenty of stiffeners for the transom, then your laminate could be somewhere around 2000-3000gsm of quadraxial oriented fibres per side and youd be in the ballpark for a minimum but safe weight laminate.

 

Oh great! Do you think I should add another layer of corecell? This foam core concept ... I don't know, seems like plywood done right is the way to go LOL!!! You can build two boats for the price of one, so build two and use the first one ten years and then use the second one the next ten years

Okay so like 6 layers of 12 oz ... The transom is VERY well braced I can not see it going anywhere, the rest of the boat will fall apart first. It's braced to the back sponsons plus the front will have bracing to stringers and deck. I will add a compartment in front of motor for fuel filters, batteries etc ... to cover the bracing.

Im still working on that, this will give you an idea


I might as well infuse the transom and other components all separately ... it would give me a chance to practice some more.

 

Groper - I can't discuss the whole structural engineering bit in the forum! I've been studying and designing structures for over 35 years (hard to admit that) and I assure you its not a black art. Transoms are always a bit of a difficult problem due to the clamping loads and inertia loads. But just using a bigger SF is not the answer. Sandwich structures are not always the answer either. The aircraft industry for instance will not build a sandwich primary structure even though they know it will be lighter. This is because they have no redundent safety or structural reserve. If the core fails the entire structure fails, if the skin crincles the entire structure fails. You can't park a plane. So each structural solution has to be considered case by case. The Volvo boats for instance use solid laminates up front in the slamming areas. No foam is up to the job in the southern ocean doing what the Volvos do. There are very good arguments for not using sandwich construction in boats whatsoever just as many to use them. Peter

 

I am not very good in the kitchen My brother is an engineer, but he is out and about, think he is in Holland right now

 

A better view .. I have not shaped those back braces yet but at least it shows how they tie in. The deck stringers and tunnel plus front angular braces not show will support the transom and provide a structure for storage and maybe a seat or live well

 

No Jorge, adding another layer of corecell wont do anything for you... just as peter used the VO70`s slamming in the southern ocean example, the foam you already have in your hull is already there, its too late, you cant simply increase the density of it as you already have your bottom laminate completed. As your boat is very light and small, M80 corecell is probably going to be alright anyways, just dont go wave jumping it in the surf and it will most likely last for many years. -Im also using M80 in my cat, which will see larger seas than your flats boat, however i increased the bottom laminate to 3000gsm to help it survive localised small impact damage and wave slamming.

Peter, did the volvos change their bottom laminate recently? As in this years race, i remember 2 of the boats suffering hull delamination up the front when crossing from NZ to south america and so still had a cored construction...

 

Got it, so density is the issue. Yeah, can't change that but I still need to glass the strakes and inside of tunnel so I can infuse another layer to entire bottom ... I feel I should after the poor first infusion.

Its pouring rain ... I think I am going to build the jig for the tunnel.

Have a good day

 

The construction is up to the designer but the boats that work have solids up front. There is a thing called rolling shear or asymetric loading of panels. As the hull panels are attached to the bulkheads they flex inward from pressure. At the BH's they have tension on the wet side and compression on the inside. The centre of the panel is opposite to this. ie tension on the inside and compression on the outside. Somewhere along the panel where this loading changes from side to side is a point where the core is placed in high through thickness shear and high in plane shear. This delaminates the core if its inadequate. The way around this is to have solid laminates at the BH connections and only have core in the middle of the panel. Some boats are going the way of aircraft where they use all solid skins and more solid stringers. This gets around the core issue. Or they use shear ties every 500mm or 1000mm along a panel. A shear tie is a laminate that goes from side to side. This stops the core zippering if it fails. The other thing that happens is that nomex is used alot and it has a very small bonding area and if its not bonded exactly right it can disbond and fail. Peter

 

I flew on an airliner a few years ago, I'm thinking it was an Airbus but maybe not. I sat over the wing and noticed there were no rivets so I figured it was a composite. On the ground everything looked fine, as we ascended a bubble started forming until it reached the size of a dinner plate, as we descended it shrank back and disappeared. I drew a picture of it's location on a piece of paper and told the pilot about it but he just poo pooed it with some ridiculous explanation, but the flight attendant looked concerned so I gave it to her and told her to take a look once they got back in the air.
I also flew on a Continental jet a long time ago and as I got on I noticed a crack in the skin, originating at a corner of the door opening and running about 5 feet over the top.
I also flew on the old Gooses in St. Croix. I got to sit in the co-pilot seat as I guess there was no co-pilot. One engine had normal oil pressure, the other one hovered at about 5 lbs. A few years later one of the planes disappeared into the sea.

 

I would have debarked the plane with the visible crack LOL!! Too bad no cell phone camera to take a pic of the bubble.

I ordered some 1/4" corecell to laminate over this tunnel jig I just built. Im going to infuse it as well. I was going to bond it to the hull first and infuse but since I decided to leave the transom out, all these related pieces might as well be infused.

 

4 layers of glass and peel ply in place. I took extra care to make sure there was no bridging, this should be a picture perfect infusion, I barely used any tape that peel ply is laid out perfectly even though it looks weird in the pic.

Also I left peelply hanging out to wrap the MTI vac hose in.

Monday I will add release layer and then resin hoses. This time its going down perfectly!

 

Almost ready for another infusion...





I couldn't find the right size cross connectors anywhere for laying out the hoses in the fishbone pattern. McMaster Carr and Cole Palmer think I am an exporter because my address is a mail house so they wont sell to me ... can you believe that LOL!!!

I made these out of a Nylon Rod really quick, they should work okay. I was not comfortable with interweaving the hose ... I think I was doing it wrong, hose would tend to pop out and at times it looked as if I was blocking flow. Have to practice that method on a panel!!





Monday I will lay the otherside of flow media and add the MTI vacuum hose and the vacuum bag ... then I need to fix my pump Have a good weekend everyone!

 

This method worries me jorge... race track along the floor to edge join is a real possibility no matter how well you think you layed the stack... If this occurs you will have huge dry spots between every secondary "bone " thats running perpendicular to the back bone. The resin will come out of the secondary bone ends and hit this race track area very early in the piece...

i personally would not do it this way... it has a strong likelihood of failure...

Instead, i would put the resin lines along this floor to side chine... pull the resin upwards to the gunnel vac line, and inwards to the center of the boat where you will use a short piece of MTI hose for a center vac point. You may need an extra pair of feed lines between the floor to side chine and the center line if the distance is too great which it most likely is. In this instance, i would mix 2 batches of resin, the first batch to feed the chine resin line, and later a second batch to feed the inner resin lines once the front passes inwards.