Cobia 24' rebuild project.

[Woodonglass]

You can do scarf joints but...there are two good alternatives. Lap Joints and Sister Joints. If your stringers are going to be 3/4" thick then use 3/8" plywood and lap them at the 48" mark and you can make em as long as you need. This drawing illustrates How to make a 16' stringer using lap joints.



This drawing illustrates how to use a "Sister Joint" But the two ends of 3/4" plywwood together and then use 1/4" plywood on either side to glue and screw the "Sister" pieces on. A 36" long "Sister" 18" on either side of the joint and use Titebond III wood glue and deckscrews will yield a strong joint with NO FLEX.



Scarfs are Hard to get Perfect and even harder to glue up and keep aligned properly. Really not needed for stringers. The above mentioned methods are proven and more than acceptable to use.

 

[zuluwarrior]

Thanks for the info Wood, been kinda beating myself up over the joint integrity issue. I haven't cut the ply for the stringers yet so can go either way.

 

[Woodonglass]

I been working with wood for 40 + years. Personally, I'd use the "Sister" joint and move on. Fast, easy and strong as heck!!!

 

[kcassells]

Went with the Hermco fiberglass bracket. Single motor mount with 30" setback. Just had him shorten the swim platform so I don't have to worry about fitment around the notch in the transom.

Tell me more about the motor mount. What are the benefits, pros, cons, reasoning.

 

[kcassells]

Tell me more about the motor mount. What are the benefits, pros, cons, reasoning.

generally speaking I would like to hear from anyone who has gone this direction. I am considering this option.

 

[zuluwarrior]

Hey kcoassells, Bermuda has a very high salinity and I was trying to minimize the maintenance factors of overall upkeep as this boat will be kept in the water for long periods. Don builds a very good flotation bracket and for me repairs would be something I could handle, I don't weld. Cost wise the fiberglass bracket is a bit higher in cost but I feel in the long run it is the better choice for me and my environment. I will make sure to post pics when I get it and after it is installed.

 

[kcassells]

Ok tx!

 

[kcassells]

I guess what I see is that the primary advantage for my boat...and yours is that their is a deck area gain. For me @ 18" to 24 ". That's alot, plus the advantage of not having a short transom/water is pretty big to me too.

 

[zuluwarrior]

Yes you are correct. I like you gain cockpit footage and I can and will be raising my deck 1 inch and there is the self bailing aspects. My biggest concern will be the balance of the boat once the bracket and motor are on there. 30" setback and a 400 plus pound motor.

 

[kcassells]

Yup...had that aspect on my mind too. In regards to drainage ie mods.

 

[zuluwarrior]

No Title

Had a late start today, shoulder was feeling achy. Took a couple of Aleeve and setup jig to make a couple of scarf cuts but first I built a couple of new saw horses. I had made the jig 24 and half inches wide so a sheet of ply cut down it's length fits in there good. As this is new for me and I was using the ply for the stringers I just took my time and cut the ply. I was able to cut two scarfs and they came out pretty good, just needed a little sanding which I did using my belt sander. Tomorrow I will mix up some epoxy and glue them together. The next two should go faster as I now know where to set the ply. The scarf is 9" long. My plan is to then cut the stringer to length and add the second layer of ply to it which will also overlap the joint. The second layer will give me my addition thickness for the transom knees.

 

[kcassells]

Feeling achy are ya? Come over here and get a taste of this freakin winter wind! No yum yums for you. The scarfs do like nice though. If you don't feel good about the strength of the scarf you can always add a butt joint pc. Looks like your right on the money.
With scarf joints, it is preferable for the two pieces to fit as closely as possible for ultimate strength. However, minor irregularities of fit are acceptable since the epoxy will have the ability to bridge these without significant loss of strength.
The amount of taper with a scarf joint is usually stated as the ratio of the thickness of the joining pieces to taper. Common ratios are 1:8 ~ 1:12; that is, the length of the taper is 12 times the thickness of the members. In other words, if the wood were 1" thick then the scarf would be 8" long.

 

[kcassells]

Hi Z,
I was just thinking...uhoh... When you go to join those 2 pcs together bind them with two pcs of ply with clamps. On the ply your going to bind with {the outside temp pcs] spray or rub with any car wax before applying/tightening and when cured the scabs should relatively come apart away from the scarf joint.
Just a thought.

 

[zuluwarrior]

Yeah I figured a 1:12 ratio so like you you said for 1 inch thickness you have a 12 inch taper so I am close using three quarter inch ply. Will let the joint setup really good before adding the second sheet of ply. Should end up with about a 40 inch overlap.

 

[zuluwarrior]

First stringer length glued up. I'll leave it for a few days to cure good before adding the second piece which will overlap the scarf joint then start on the next one. Need to take my time and not race the process though:joyous:

 

[kcassells]

Well at least you got to it today. My palm sander pooped the bed. Velcro thingeys won't stick nomo! saw a couple of quick fixes like glue on 2 sided velcro so the pads stick or buy a new pad from the mfg so in either event momoney!
Not that you have to run fast but why are you thinking to wait a few days? Your using poly or epoxy...I forget.
And oh yea...you're right just take your time cause its still there tom. God I wish I lived somewhere warm year round.

 

[zuluwarrior]

Work, just won't have time during the week. Mind you I will check it when i get home from work Monday evening and should be able to pull clamps and have a look. Using epoxy for clue up.

 

[zuluwarrior]

Hello All, still alive and just started back with some work on the boat. The weather has been horrendous over at least the past 3 weeks then I came down with of all things, shingles. Man that is some painful stuff, out of work for 3 weeks, just getting back to myself again. But some good news is that the laminations for the stringers are complete and I will be moving to making the templates. They are approximately 12.75' long. The scarf joints came out very nice and I held a panel before it was cut down(16') up by one end and gave it a shake to flex it and these things are solid. Very happy with the results. And Wood is correct that it did take a bit of fine tuning and fiddling to get them right but very pleased. Also, my transom bracket is complete and id due to be shipped sometime next week. With daylight saving time fast approaching I'm looking to make some good progress.

 

[kcassells]

Zulu,
Great for you! Can't wait to see more progress. You have been quietly kickin arse!
Good, really good to hear form you. Hope all is well.

 

[zuluwarrior]

Yeah KC, house is repaired which is a great burden lifted and did some demo work today for a couple of hours. Need another couple of good weather weekends to get some grinding and prep work out of the way. Really need to organize my supplies to see what I have and how much roof it and what i need. Things are a bit scattered between my mudroom, shed and boat lol