My transom fell off

It is Pronounced See-Booo. It is a very large city (2 Million) located in the Philippines and the name of the island where the city resides. It is one of the most beautiful places on earth. Also has some of the worst slums too.


CEBU

 

Cebu,

Do it right or don't do it at all. You've already declined two of the best so eventually at this rate the help you are going to get is going to be rather poor.

 

I must apologize... The post, if you re-read it, is only a fictitious example meant to show how a question might be phrased so that it could be intelligently answered here on the forum.
I see quite often that the thread-starter doesn't provide enough info to get one's teeth into ("I'm building a boat of my own design from oatmeal and I need to know what kind of keel I'll need...")

 

I, for one, have difficulty believing that Cebu could actually be any type of engineer. How could you have a backround in the engineering sciences and reject any and all attempts to communicate in terms (like laminate schedule) that NA's or "marine engineers" can understand? It just doesn't make any sense to me.

End of discussion.....

MIA

 

I can’t believe you missinginaction are an engineer, laminate schedule is not a term used in my field of study. I have two BS degrees - BSEE (Electrical Engineering) and BSCS- (Computer Science) and I have worked for 3 years in the mechanical engineering department at Rockwell Collins Avionics. I am currently a Network Engineer working in Microsoft and Cisco house. I may not have all the Mechanical - Marine Background as some of the people helping me. That is why I am here requesting help. And If you were an engineer you would know, very few engineers know a lot about other fields of engineering aka Aeronautical, Software, Chemical, Nuclear, Electrical, Mechanical, Industrial, ect... So it should come as no surprise to a real engineer, that I do not know terminology specific to a different discipline of engineering.

I have already stated I’m clueless as to Marine Engineering and design and also I have no real experience with large-scale fiberglass projects. I simply stated I am an engineer so that those wishing to help me would not hold back because I have the ability to grasp a new engineering discipline.


ThanX

Cebu

 

Let me repeat myself:

I am an engineer (industrial). And when speaking with engineers outside of my field of study I don't get all pissy when they use a term I don't understand. I have never seen another engineer do that either.

 

a cebu, if I am not wrong, is a four legged rumiant with short strong horns living in the asiatic south east ..............

 

Engineers are real little more then researchers that can draw in 3D. The hall mark of good engineers is that they are happy to "look it up" and more importantly, tend to "keep up" with new innovations, techniques, on going research, testing, industry trends and disciplines. If not they fall behind and lose the "edge" that made them (as a commodity) a viable interest in the first place. Who wants to employ or commission an engineer that is using dated techniques, material choices and thinking, not to mention an engineer that can not or worse, will not "keep up"?

 

Transom scantlings

Cebuano,

The thickness of the transom that will receive an outboard motor is usually dictated by the motor mounting bracket. About 1” to 1 ¼” for smaller outboards in the 25 to 45 Hp. Bigger outboards needs 1 ½” to 2” transom thickness.

Transom height (the distance between the top of the motor mount and the bottom of the boat) is dictated by the lateral position of the “cavitation plate” in relation to the bottom of the boat. The cavitation plate is a small wing (like a small surfboard) attached to the strut housing located just above the propeller tip. Manufacturers specify that this mounting plate aligns lower than the bottom edge of the transom. 1” is generally recommended but others have experimented with this for different results. Positioning with its merit was discussed in this forum some years back. Transom height is also dictated by the length of the shaft of the motor. There is what we call a “long shaft” and a “short shaft” and is self explanatory. To be sure, check your motor specs and the specified mounting distance.

Transom are usually angled outward from the vertical. 100 to 105 degree is typical. Adjustment is possible thru the mounting bracket but consult the mounting installation instruction to build the optimum angle.

Transom is usually thick and made of wood. Thick to increase stiffness, wood to absorb resonance. It is sheated in metal or “fiberglass” depending on the material used to build the boat. Marine plywood is generally used as it is stronger. Others prefer high density foam core in the order of 250 kg/m2 but requires metal anti compression bushings where the bolts go. To build up thickness, plywood/core is laminated together, usually with epoxy. Make sure you drill 1/16” to 1/8” holes spaced 6” apart on the core/plywood that will be laminated over. This prevents air entrapment when gluing.

Solid glass is sometimes used but as is, is usually heavy. It is made thin but supported by a lot of grillage structure.

If you are going to use poly resin to encapsulate the plywood, do not give it an overcoat of epoxy but if epoxy is going to be used for lamination, you can. Edges must not be exposed to elements so coat it liberally with resin. If the hull is metal, bond it with industrial epoxy.

The transom (with an outboard motor) pushes the boat so to speak. The load must be transferred to the rest of the boat by coupling it with the major structural component of the boat. If you look at the cross section of the boat from the transom, You probably have a keel stiffener based on what you reported. There is probably two more secondary longitudinals running the length of the boat located port and starboard of the keel stiffener. Most probably, you also have a side stiffener, at least one on each side of the hull. This is where your transom must connect and reinforced with a bracket.

The transom needs stiffeners. You intend to use two motors, so that divides the transom in two. Good. The transom can have a central stiffener that goes all the way to the top and connected to the central keel by a bracket. The bracket depth is about 1.5 x the depth of the longitudinal it is attached to. If you have two secondary bottom longitudinals, it must continue to the additional vertical stiffeners of the transom. It must also be bracketed. The secondary vertical stiffeners might not run the full height of the transom as it will interfere with the motor mount.

Perhaps an overkill but if the transom is thin, you might need a horizontal stiffener that aligns with the side stiffeners. If it interferes with the motor mount, the full length can be omitted but at least have one in the main vertical. From side stiffener to the transom, fix it with a bracket. The rule is whenever there is a discontinuity or cut of a (major) structural member, it must be bracketed. Bracket, brackets, is the norm.

Attached are some graphics to help.

BTW, get a copy of Naval Architecture for Non Naval Architect book available from SNAME, Pavona, CA. It will help you become conversant with boats. It does not contain fiberglass though.

 

As for me, I would go with Coosa and an appropriate layup on each side.

In my case, I left the old skin and laminated 4 layers of biax, then vacuum bagged 1" Coosa Bluewater, then 4 more layers interweaving corners with hull side layups.

I toped off the outside with a Carbon Fiber 24K skin for aesthetics. I have attached the transom core where the cut-out for the surface drive was made. There are many additional layers from the hull bottom and stringer overlaps.

The new stringers were filleted to the transom and a trim pump platform also served as corner bracing.

I am not a pro, but I had good advise and help.

 

Yeah right ! could expect a nonsense sort of an answer like this from a stuck up toffee nosed dick head like you !! The man asked a question so give a non technical simple straight forward answer Ops sorry thats beyond your comprehension and below your dignity !! Professional dick head !!

 

Lonely Man Tunnels

So I see by your post that your are now living in China. Luckily for you your foul mouth and obviously mediocre education are not as easily discerned by people who barely speak English.

As your response is unnecessarily aggressive, I can only imagine how your rancid personality has made your life more difficult.

My personal opinion is that when a professional, or someone with a better understanding of the topic, takes the time to offer advice; rather than berate him for not de-educating his vernacular; pick up a book and look up the 3-4 words that are not well understood. That way you can actually "learn" something.

"Tunnels" You called people dick-heads. This aggressive tone should be reserved when you are standing toe to toe with someone. Not from the safety of your dorito laden keyboard in some third world hovel. Most people with balls do not talk tough on the internet.

Cebu, you gave everyone your resume relating to all your "amazing" capabilities (no job offers here); but after extolling your capacities in every other field with the exclusion of Nuclear engineering and boat design, you then proceed with an elaborate and detailed description of a transom design that most people with minimal access to online resources would find amusing if not silly.

Instead of laughing at your approach; Rxcomposite took the time to give you some very useful information and you essentially complained because he did not dumb it down enough. This is particularly amusing since you spent so much time talking about how talented you were in other engineering disciplines....

As someone NOT suffering from head trauma who has access to the internet I appreciate RxComposites efforts to advise and help. It is people like him that make BoatDiesign forums useful and a valuable tool for those who wish to "LEARN" and develop comradery with other people who share the love of the sea and boating.

"Srimes" struck the nail on the head. Why would you get "pissy" when someone uses appropriate terminology when trying to help someone?

The reason is simple; most people who proudly call themselves engineers and consider themselves intelligent do so with the sole intent of branding themselves and not as a matter of fact. Their greatest achievement is a piece of paper indicating the were able to sit in a classroom long enough to extend to themselves the hollow privilege of claiming they are better or smarter than someone not sharing the same space for the same period. For them, it is not about learning,self accomplishment or discovery - it is about consoling their own insecurities. This low order mentality seems to have manifested Tunnel and Cebu.

My coffee is now gone and so am I.....

Thanks for your assistance RXcomposites

 

ooops Did i touch a raw nerve ?? .
Third world hovel !!, you need to take you blinkers off and clean the moth ball out of you ears !! This is the most modern ,cleanest and futuristic place i ever seen and or been in during all my travels and countries ive been to bare non . What you see from the media is not what its really like !!!
Looking through posts from time to time theres alway obnoxious comments from your friend just about every post he answers he pisses some one off and yes some people do get offended , so time to return the flavor of the comment .
I will say hes has or had a sense of humor reading some of the funnies posts from a while back !!
Sorry but he is still a obnoxious dick head , probably has bits of paper in dusty frames hanging in his kennel !!
Yes working in China and is an interesting place to be . in the time Ive been here i have not meet any stuck up toffee nosed people yet !! Not even the visitors we have fit into that category .

 

Thanks for the nice words Chris. I wrote it in a general way so others would respond how they approached it in a different way like you did. That is what makes the forum healthy.

Did I miss some post? Cebu semed to have simply vanished. Perhaps he did not even look at my post. I was trying to help.

Sad to say but sometimes people behave differently when they receive a beating.

 

Chris summed it up in a nice way.

This Forum would be even better than it is already, would more people grasp what he said, and act accordingly.

Tunnels was regularely attacked by me for making false and dangerous statements, I can understand that he does not like me. But that neither makes his dumb drivel better, nor does it help others, in search for help. see:
http://www.boatdesign.net/forums/fi...ebates-heated-remarks-34526-5.html#post398670
which was, and remains valid. He sells his wrong and dangerous opinions as "advice".

The "cebu" screen handle seems to be just another one for tunnels, btw! His very first post (below the post linked above) is almost safe proof of that.
It is unlikely that he will return on topic here, he never did when contradicted by professionals. (except for insulting of course)

Regards
Richard