Designing A Cantilever Platform Using Epoxy-Glass Fiber

Just make sure you add in a couple nice sturdy gussets to take the load and transfer it into the hull. Just a plain cantilever would most likely fail without gussets.

Hi RVZ717

Thank you for the suggestion. It is to be mentioned here that the Hull of the Dinghy is a new composite system that has excellent strength-economics properties. However, drilling holes to accommodate bolts. screws may create long term weakening of the structure. Such a condition would necessitate that our cantilever design would have to be innovative, and fabricated without the "normal" gussets or "slings" that require bolting or screws.

I think it can be done easily enough. But I would include at least one, but probably two, triangular support fins, made from the same material, and fabricated at the same time, coming off the bottom of the platform at approx. a 45° angle, and tying into the back of the boat below. Otherwise it is likely to crack.

Depending on the availability and cost of materials, this could even be made from plywood as a form, and wrapped with the composite.

PS- The last post wasn't up when I started my reply. Gusset is a better word than fins, for what I was describing.

You give the weight of the motor but the thrust must also be a consideration.

I suggest that the platform be constructed integrally with a upward gussets to a plate, to match the opening surround, that can be glued/adhered on the inside of the stern.

Alternatively, make an assembly that can be dropped down over the stern, with plates inside and out, with gusset plates from the platform to the outside plate.

We are looking at an innovative "SKIN" system as per illustration below:

Expert comments and suggestions are solicited

I like your ideas, but I do feel that some extra (strong) stays each side will be needed for 200Kg. loads......maybe even two more going to the lip of the boat as well (in Red).

Hi Andy_Germany

Thanks for the good suggestion. I like the suggestion

Our first trials are being planned using an engine having total weight of about 100 Kg. Our computation of the shear load (at a 40 Factor of Safety) shows that the "joint" that is weakest in this design would take up dynamic load of 750 Kg (uniformly distributed at a central region). Let us see how the first trials go off

You seem to be commenting for a static load, firstly the motor will propel the boat will make extra loads in both Ahead and astern movements, these are very important to fully plan for.

Secondly, vibrations can bring loads many times the static load, 20 times is not an exaggeration for a good quiet low vibration motor. The vibrations will concentrate the movement of the joint.......to make it vibration resistant will make it many times heavier if there is no extra support as I demonstrated....

Do not forget a safety line to stop the motor dropping off and sinking if something untoward happens and make sure that you can easily cut the ignition as ingesting water usually wrecks an engine completely.....

Let us know how you get on.

Thank you again

Your suggestion is well taken; and also those of: kramarat, passingtongreen and that of jerry0 ..jerry0's suggestion is being immediately carried out and we shall be trying the "sea-run" of the dinghy in a couple of days

Thank you all for the support. Would definitely keep all the discussion group people informed of the matter

pvhramani.

Do not forget a safety line to stop the motor dropping off and sinking if something untoward happens and make sure that you can easily cut the ignition as ingesting water usually wrecks an engine completely.....
If the OP is really going to use JerryO's suggestion of a couple pieces of angle iron of unspecified size, with unspecified fasteners and fastener spacing, through an unspecified laminate structure, then we can assume that the platform will fall off under the load, particularly because the transom corners above the cutout are weak. Given that the motor will fall off, taking some transom with it, probably better to let it go, rather than have it helping to sink the boat. Better chance of having a couple of the people on board survive.

LOL!

How true!!!

2 angle irons bent at 90 deg. fastened from inside of back over top of cantilever. Flat sides to back and top. Ribs up.

the OP wrote "using EPOXY-GLASS Fiber Composite?"

so I'm not sure how angle iron matches this requirement?

Rather than attached gussets using screws or bolts, why not attach them using epoxy resin and fiberglass matting? Basically you would be "gluing" them to the transom and support feature.

all I can say is Wow! ga

That is a really good idea (I like the CAD drawing you have done, clear and simple), its what many lightly built yachts, especially smaller multi-hulls since at least the '60s, though it may have also been in usage even earlier......As weight is a problem for such craft, especially directly on the stern......

Also, outboards on the stern can spend more time out of the water than in when the sea is a bit lumpy (been there done that and not got a T-Shirt to show for it!! Both on small sailing and fishing boats.)

They did that so that they can have an engine that can be:-

1) quickly removed or just raised for good sailing qualities

b) to allow easy (cheaper) repairs in a shop when needed and not buried in a boat

c) plus its a complete unit in itself, doing away with shaft (and alignment problems), leaks due to bad sealing glands etc..

d) it is also cheaper and lighter than a "proper" inboard engine.

e) take far less space on-board

f) takes the weight into the middle of the hull (like an inboard) and puts the propeller in deeper water for more effective drive (even deeper and better than the average inboard motor does with its propeller).

g) far fewer holes piercing the hull even counting the one big hole, which is easy to both seal and to fit a plug in when sailing is more important than using the engine, though this is probably not the case here.

thanks andy (sadly I didn't invent the idea)

there is also a story/theory (amongst many) out there that Noah's Ark had an internal well, which allowed it to survive tsunami sized waves nad not break in half, because the design reduces stress/ increases strength across the central axes. the theory postulates that if a large crest is positioned amidships, and bow and stern are in the air, a large bending moment is put upon the vessel, with maximum effect occuring amidships, which the well eases.

chris

Which is quite true. Having been on large passenger ships and 10 years in the Royal Navy, I have seen how steel hulls twist in a heavy sea.....

The Queen Mary (the one parked in California somewhere), according to my father when he was on it in WW2 (far faster than the U-Boats!), the far end of a corridor would move down and up and completely out of sight each time a big wave passed under her!!!

wow... kinda scary.

as to being faster than a u-boat... I think that is like a duck being faster than a shotgun... but not the pellets. It would only be a matter of time until the hunter gets within range, and is able to lead the target properly.

cheers,

chris

To prove you wrong, we parked the Queen Mary in Long Beach, California many years ago...... Its still there!!

It was as fast or faster than most of the torpedo's of the time (when they were set to very short range high speed, not long range low speed!), only a few could exceed its speed, but never at long range!......it would have been a very lucky submariner that a) saw it and b) got a shot at it and c) hit it. No one was that lucky!!

She was timed on two particular voyages over the Atlantic, where she averaged over 30 Knots in both directions!!! The fastest passenger ship afloat at the time.

Look here for a list of Torpedoes, speeds and distance to run here:-

http://en.wikipedia.org/wiki/List_of_torpedoes

You will find that not many have a decent range at a speed above that of the QM!! At least not up to the 2nd WW....

You can read a short history of the ship online which includes some of her wartime adventures, but a book would be far better:-

http://en.wikipedia.org/wiki/RMS_Queen_Mary

thank you!

Friends

We have made the maiden Sea run trials on June 28, 2011 at one of India's Eastern Coast Ports ... VISAKHAPATNAM. The illustration photos below show some initial sequence of the dinghy entering and sailing into the sea

The sequences are as follows (from Top left to right; and on next level too from left to right):

(i) A 10 hp Diesel marine engine is being fitted with an 8 ft long propeller shaft on the CANTILEVER platform, specially designed and fabricated (engine + shaft wt = 90 Kg)

(ii) The engine fitted Dinghy is being "pushed" into the incoming waves

(iii) The engine is started and the dinghy is pushed further into the sea; six fisher-folks are getting into the dinghy

(iv) The dinghy negotiating a 2 m incoming tide, before moving further into the sea

The "audacious" cantilever Platform Design for the Engine mounting is presented below:

A more close up "real boat" arrangement is shown below:

(Note: The Cantilever Platform is strengthened by extra fins on the sides)

There was about an hour of sea rides, without going deep into far off sea. A few rides were made with the students who participated in the Development of the Boat/ Dinghy (The last photo shows some students in the dinghy, getting ready for their maiden sea ride in the dinghy built by them).

The Cantilever Platform Design seems to perform very well, and we shall study the performance for more days

pvhramani:

From when you first posted your initial inquire on 06/24/2011, to doing your first sea trial on 06/29/2011 , impressive.

Friends

When I first began this discussion series, it was my intention to interact with different engineers and practical technologists/ technical personnel through the forum of CR4. While it did generate some initial subject discussions ... later turning into some "noise" and "ridicule" ... the heat and dust suddenly seems to have stopped, after the news of the Sea-run trial of the Boat was presented (with photos and illustrations of the cantilever construction system).

I thank all the friends who participated in the discussions. I hope to learn more and get some more insight into the practical aspects of the Designed Cantilever system, over a period of a few months of 'on the ground observations'

Here is a close up of practical sea run of the boat (seen on the cantilever platform side):

If I were responsible for designing this boat and running the sea trials, and my insurance company saw this picture, they would cancel my insurance. This would be true even if the people outside the boat were experienced naval workers. But with them being students, my insurance company would consider this gross and willful negligence. This would be the case, even if the engine were a conventional outboard in which the position if the prop does not vary a great deal. Even then, the prop must always be in neutral whenever you are anywhere near people in the water.

The issue, of course, is that you have an unguarded prop in close proximity to a student. The prop, because it is mounted on a very long arm, can move a very large distance sideways, toward the student at the back of the boat. Clearly there is wave action, and it is easy to imagine many scenarios in which the person holding the tiller, who is not looking at the student in the water, could be thrown to the side pulling the tiller inadvertently, putting the prop even closer to the student in the water. The student in the water could be knocked off balance by a wave, and thrown into the prop.

I understand that we are from different cultures, and that the US is famous for being unusually worried about product safety, but why put students in harm's way unnecessarily?

I notice that you call this a "cantilever" but your bracing makes the structure no longer a true cantilever. In the picture below, platform deflection will cause a force along the line in blue. This force will cause the transom to flex as shown by the red arrow. The portion of the brace above the blue line has little beneficial effect on the overall structure: that portion adds weight, consumes expensive materials produced at high environmental cost, and interferes with being able to angle the motor to the large angles that could be required in slow, close-quarters maneuvering.

If these braces were triangular and below the platform, then the fore and aft component of of the bracing force would be fed into the hull bottom, which cannot flex significantly in the fore and aft direction. (the forward edge of the platform at the transom may also require bracing. Placing four such braces would provide better support near the load of the engine, so that the platform would experience less bending athwartships, reducing fatigue and the probability of eventual delamination.

In the US, modern wooden boats are commonly built with plywood or timber covered in a layer or two of fiberglass cloth. Fiberglass mat is never used in such boats, because its strength is too low, it gives a very rough finish if not laid into mold, and it absorbs too much epoxy, which is considered expensive here. Fiberglass cloth saturated in epoxy is clear, so such a boat can be varnished if desired. (The inside of the boats below are varnished; the outsides are painted.)

Boats constructed this way are light, (the blue boat pictured here is 20 lbs, the red boat is 25) durable, can be pretty to look at, and use a relatively small amount of epoxy, the coating inside and out being typically .010" (1/4 mm) thick (and with about the first 1/2 mm of the wood being saturated with epoxy (maybe 25% epoxy content?) Given reasonable care, such as your students could master, the surface can be very smooth, leading to good hydrodynamic efficiency. In the US the impediment to building a lot of these is labor cost, so wooden boats are considered a specialty item. I'm guessing that in India labor costs would be less of an issue.

I hope your sea trials continue to be successful, and urge you to think about all the things that can go wrong -- it's what engineers do. Did you do static testing of the platform?

This type of engine and prop are very common in the far east, especially Thailand. I do believe over the last 50 years or so they are now seen all over the world......

The prop shaft is quite long, longer than it appears to be in the picture....

The vessels are quite fast and very maneuverable!

Safety considerations are of far less importance in many countries.....

In the US we call them "mud motors" -- useful in swamps.

Hello Friends

A few things need to be presented here to explain some facts:

1. This Project (of developing a sea-worthy Boat building material) was undertaken to showcase how "CLEANTECH" methodology could be the starting point for Optimum Engineering Materials formulation and design (please see the new write-up series: OPTIMIZED ENGINEERING MATERIALS THROUGH CLEANTECH)

2. Another objective of this project was to showcase how commercially useful Technologies/ Products are developed (and optimized) ... starting from a mere IDEA through Concept/ Bench-Level Technology till Final Prototyping

3. The entire project of sourcing new materials systems for Wood/ Steel substitute and converting the same into a practical Boat/ Dinghy were to be completed within a time-span of just three months (April 1 2011 to June 30 2011) ... The Sea-run trial of the Newly developed Dinghy was conducted on June 28, 2011 ... two days before "deadline" date!

4. The following Technical Procedures were involved: (i) The conversion of the vegetation resources into specialty Composites to substitute wood/ steel/ regular fiberglass; (ii) Testing the composites for Tensile strength, Bending strength, Elastic modulus, specific weight; (iii) Designing a production process and fabricating the Boat/ Dinghy (based on approved design); (iv) final study of sea-run qualities of the boat

5. While the fabrication works had the total involvement of Engineering Students (under guidance of experts), the final sea-run trials were conducted by highly experienced Fishermen who go for "deep-sea' fishing

6. Since this project is a fore-runner for more refined and improved design and fabrication methods, many of the systems would be further developed and improved over the next few months, before we finally arrive at the Optimum Engineering material systems for the New Boat Construction materials

More specific details would be presented in the new write-up/ discussion (Optimized Engineering Materials ...)

oh look all the terminology has changed yet again

no more APIX/Agrobiogenic? [which also had a prototype boat, 2 or more years ago]

signed

Noise

Hello

Please visit:

1. http://agrobiogenicscleantechpvtltd.com/

2. http://zerowastezerocarbon.wordpress.com/

This is in continuation to the earlier thread ... leading to Optimized Engineering Materials ... There is new discussion added here: http://cr4.globalspec.com/comment/750225/Re-Optimized-Engineering-Materials-Through-Cleantech

Your second link was barred to me, can you help?

it's an expired classified ad

enjoy

signed

Noise

That was just 3 empty boxes for me! What happened? Or has my PC got a problem....?

it must be something with the links

one more time after saving to my pc

may be a problem with Andy's resolution setting.

It does come through on mine.

sometimes old links will give our overseas friends trouble with permissions

I think Chris was interested in showing the simple method of motor mounting which keeps the weight down low, not trying to rip the back of the boat off or causing the boat to be wider to maintain stability....

some waxed or greased rope or rags inside of a piece of pvc pipe acting as the stuffing box [seal]

steering is accomplished by the use of a canoe paddle as a rudder by a passenger or the throttleman

a pirogues are very good in extremely shallow water

Looks like I have a new hobby

I have the Australian marine flag to start with.

Great link Chris, thanks.

It does on mine now....the second version was great.