Structural Concerns

[G DANE]

As some of you know, I´m in the process of rigging a 17' runabout. I started spring 1 1/2 year ago, but had to take a "little" break rebuilding my house. Now to the subject. This boat is new, was never in water. I do not know where it was moulded nor by whom. <br />Last night I was going to turn it upsidedown to add supports under the cloused bow. ( I earlier added 7 bulkheads in bottum ) I discovered two persons could actually lift the hull from ground. I know I can lift 200 Lbs in that height, and my B.I.L. is somewhat like. This was all I could manage.<br />From my drilling, working etc I´v seen glassfiber is like only 1/4" thick on most of the boat, Except from parts of bottum - 5/16" and transom - MUCH thicker. Floor is glassfiber too with a kind of core material, the upper shell goes all the way down and rests, screwed to bulkheads, kind of a boat in a boat, of coarse a much lighter construction than usual wooden floor. Transom only has wood in the middle like an i/o.<br /><br />My question is: How thick are normal boats ?? How much does a naked hull usually weigh ?? It is 6 1/2' beam at mid of hull,and 17' long. It will be powered by my 115HP Evin. Will a boat that light be strong enough ?

 

[mred 2436]

Re: Structural Concerns

G Dane i do a lot of work on older run abouts usually late 50's to early 60's, and i have seen alot of variations in hulls and support designs. the most important thing you can use to determine what your boat is designed to handle is the capacity plate. i also need to know how your transom and stern area is designed. does it have a splash board molded into the gunwales? does it have support braces from floor to transom? is your hull a full displacement design ( smooth ), or is it ribbed?<br /> you say the floor has a core material? can you define that more? most fiberglass hulls are sealed double hulls, to give the craft floatation in the event of swamping, and some were filled with floatation material. in any event, do not drill holes in your floor unless absolutely necessary, and if you do, make sure they are sealed for two reasons. one, if there is no drain hole for this area, it will eventually get water in it. and two, if you would happen to puncture your hull, your boat will sink much faster than you will want it to!

 

[18rabbit]

Re: Structural Concerns

G Dane – you don’t mention the year of your boat but modern boats take advantage of differences in resins to get a trade off in the cost of materials vs structural integrity. Some resins flex more and lighter boat may be designed with this in mind. Some resins are more rigid and prone to failure if flexed so these boats are built with more stringers, etc.<br /><br />Probably more than you every really wanted to know about resins and fiberglass for boat design:<br /> http://www.marinecomposites.com/ <br /><br />The whole book is there, on-line…free!

 

[G DANE]

Re: Structural Concerns

This boat was build in 1996, it has no rating plate. <br /><br />According to ACG rationg formulas, it is OK for 100 HP.<br /><br />It was assembled without stringers, apart from one in the middle, and one bulkhead, made from 1/2" thick glassfiber, when I bought it, I cut floor out, glassed in 7 bulkheads on advice from a boatbuilder, and glassed the floor back in. Floor is a part of upper shell, as mentioned. I will now add knees (gussets ) up to transom, and stringers. The mentioned core material is white stuff, apr. 1/2" thick very hard and stiff.

 

[G DANE]

Re: Structural Concerns

THANKS for the link - GREAT INFO.

 

[G DANE]

Re: Structural Concerns

Mred2436<br /><br />It is definately planing, it is deepV with ribs.<br /><br />Transom is as described in provious reply. Stil a little concerned about the thin glassfiber and low weight. If there was a place I could uplaod pictures I could take one and upload.

 

[mellowyellow]

Re: Structural Concerns

cheers mate,<br />floatation foam will add a lot of structural strength.<br />is there any foam under the floor?

 

[phatmanmike]

Re: Structural Concerns

gdane, youve help me out many a time, so now i can try an help you,,,, as for the weight of your boat, i have a 1986 bonito center console, 16,6 long, and 72" wide, 20 inh transom, dry wight including console is 650 lbs... your size seems very close to mine and i hope this helps you out some....

 

[Spidybot]

Re: Structural Concerns

G dane. Could you post a pic? Being i your region my archive may have something. It is quite common that well known brands and models moulds are re-used by smaller or private builders if the manufacturer go down.

 

[G DANE]

Re: Structural Concerns

Thanks Phatmanmike - thats clouse to mine, but mine is a good part lighter indeed. What max size motor is yours rated fore ?<br /><br />I will try to get a place to upload a picture, maybe someone can identify it. The guy I bought it from, ment the model to be named "Clipper" if that rings a bell UU.<br /><br />MY: There were styrofoam blocks under the floor, I threw them out , didnt want it rattlin around. No foam. Thanks for all replies.

 

[mellowyellow]

Re: Structural Concerns

blocks? no strength added there. you can install<br />expansion foam that bonds to inside of hull for<br />a bit more strength. and BTW, my 16' bowrider<br />weighed 1050lbs.

 

[mred 2436]

Re: Structural Concerns

g dane : with seven bulkheads and the floor reglassed in , i'd say you"re excellent for floatation and with the gussets from floor to transom, there should be enough support for engine thrust. my only concern would be the stress on the transom while the boat is being trailered. i would recommend the use of a transom saver, just to be on the safe side.