67 flatback project - father and son

[ncrowe]

Oh, and you just need to grind down to clean glass - don't overthink it - post pics and we can advise. You can glass over 24 grit results in some applications but you might need to be more gentle in some areas with a 80 grit wheel. The wheels last a long time. They don't like uncured resin though (don't ask how I know this) and they are ruined after that.

Thanks Rick - for the benefit of the group I decided I'm going to do a little test - and I have so much grinding to do on this hull I might as well share

I got that 7" grinder from HF - also have my 4.5" grinder - also got a belt sander with 24 grit - and I've got a bunch of different types of discs to grind with - I also ordered ZEC 16 grit discs https://www.amazon.com/ZEC%C2%AE-Litex%C2%AE-Grinding-Wheel-Heavy/dp/B00C9FWW0A/ref=sr_1_2?keywords=zec+16+grit+7%22&qid=1575555853&s=hi&sr=1-2for the 7" which I've heard on the wooden boat forums are the best - I'll record the process and show the results - I'm a huge fan of finding the best way to accomplish something with the least amount invested







Not Sure if this one will work, but has a 90 day guarantee through HF that if I don't like it I can return no questions asked

[RickK]

Make sure you keep all of your fingers, limbs, knees and those of your son away from the very coarse wheels. They can/will damage anything they touch even for a split second, like when you set the grinder down and the edge of the wheel touches. I would start the process with the diablo flap to get used to the torque the 7" will generate from the big wheel. I think you'll be pleased with the performance of the 40 grit flap. Oh and buy a good mask, not one of the paper ones, buy one with replaceable filters and get good goggles. Move a lot of air with a good large fan.

[ncrowe]

Make sure you keep all of your fingers, limbs, knees and those of your son away from the very coarse wheels. They can/will damage anything they touch even for a split second, like when you set the grinder down and the edge of the wheel touches. I would start the process with the diablo flap to get used to the torque the 7" will generate from the big wheel. I think you'll be pleased with the performance of the 40 grit flap. Oh and buy a good mask, not one of the paper ones, buy one with replaceable filters and get good goggles. Move a lot of air with a good large fan.

Thanks - I don’t let my son do any of the grinding - he’s only 11 so he’s not allowed to use any of the cutting or grinding tools - he’s good with a drill and pressure washer.

Got my tyvec suits coming - have the big fans - got some awesome gloves that literally go up to my armpits - got 2 separate masks - anti fog goggles - so as soon as the suits arrive I’ll be grinding away.

I did throw the diamond turbo cup wheel on the grinder to do a real smal test patch - it’s awesome on the bonding cement

Hopefully this weekend we can get the transom done - but it’ll depend on when the tyvec suits arrive

[ncrowe]

Okay - so results are in...... took a little time to get all the material in, but yesterday got on the grinder and took care of business.

So if you are grinding and all you have is a 4.5" grinder - to remove large amounts of material (like bonding cement for stringers) - you'll want to use the diamond turbo cup from harbor freight - its meant for concrete. Not only does it chew through material, it also leaves a flat surface thats relatively smooth. If you are removing gelcoat, use a 5" backing pad and resin disc, makes really short work of the gelcoat and is easy to control depth. If you don't care about how long it will take and want to stay with the 4.5" grinder - flap disks will work, but for heavy material removal you'll find the flap disk will wear. In my very humble opinion the ZEC disks are the way to go. They do not clog at all, and they easily run through whatever you put in front of them.

Fr those who want to go 7" and make really short work of removing lots of material - ZEC disks come in 1st place again - I was able to remove all the material and get to glass in less than an hour



So there you have it - ZEC disks for the win - I'm going to finish up preparing the transom today and I'll show progress

[mshugg]

Thanks for the report.

[RickK]

Ditto with mshugg.
The ZEC looks to be a beast. What distance from the transom (inside) do you show here?18" is a minimum so you have room to work and the overlaps of glass will work out to at least that if you use 4",8",12".

[ncrowe]

Ditto with mshugg.
The ZEC looks to be a beast. What distance from the transom (inside) do you show here?18" is a minimum so you have room to work and the overlaps of glass will work out to at least that if you use 4",8",12".

Welp - just measured and I'm at 15" - more grinding!

[RickK]

When you start laminating the layers on the inside of the transom you'll be laying glass on the hull bottom and hull sides and usually use 4" 8" and 12" overlaps, then new core and then 3 more layers with the same 4" overlap. So you'll need to either cut back the side liner or pop it out of the hull totally.

You'll also want to add a pipe because your low point is going to change and the water will pool up about 12-15 inches in front of the transom.

Here is a link to where I explain the thought of the PVC pipe
http://classicaquasport.com/smf/index.php?topic=13148.msg133124#msg133124

Here is a link to where I show what is the actual problem
http://classicaquasport.com/smf/index.php?topic=13148.msg133556#msg133556

Here is a link to Hawgleg's rebuild that shows the PVC pipe installation to keep a drain at the new low point of the boat
http://classicaquasport.com/smf/index.php?topic=13148.msg134262#msg134262

[ncrowe]

Thanks for all the help guys - just want to make sure I'm good to go - please take a look at the photos - I ground back to 18" and there is no liner in the boat - there are a few spots of filler in the corners, do I need to remove it (its in areas I'd be making the filleted radius)

[Tampa Bay Mike]

I would say you are good to go. Just give it a good acetone bath first

[Capt. Bob]

 

[RickK]

Looking plenty clean now. Cute pup - I wouldn't want to sneak into your back yard to take a peek of your rebuild
So, have you decided on the transom design? If you want to mount a motor directly to the transom that you can trim up all the way then you really only have a notched transom option for a 20" engine or a 25" motor if you decide on raising the transom 5". A full transom with only a electric or hydraulic jack plate will be a problem, it won't raise enough to trim above the steering or hydraulic line if using a bay or seastar hydraulic steering system. Reports have posted that the hydraulic lines can be sheered off  because of the transom being in the way. Otherwise the options are a fixed bracket or porta-bracket that allows the motor to tilt up while being off the transom. The latter being a heavier transom because of the offset of the motor from using a jackplate or a Porta.

Whichever transom you choose, now is the time to figure out the length and width of each layer of glass for the lamination of the new transom skin to the hull sides and hull bottom. Using melamine across the back to work from.  The way you cut your cloth/resin it after that depends on the end result. I mounted a 1x2 across the top of the hull sides at the very aft and clamped the 3 layers of 1708 that are layered with 4,8,12" pre-cut, to the 1x2. I folded the first into the boat and  I trimmed and pleated in the corners. It really doesn't matter if you go with 12/8/4 or 4/8/12 as they'll all be done wet on wet with the fillets being done prior. Flip in the next layer and trim and then the 3rd layer. Then flip all the layers out of the boat, squeeze in and form all the corner fillets with thickened resin (bottom edge and hull sides). Now is the time to glue in the PVC pipe using thickened resin. Let the fillets set up so that pressing on them don't allow them to move. then mix up enough small resin mixes to continue laminating the 1708 for the new skin.

[ncrowe]

Well we got the outer skin done yesterday - used 3 layers 1708 for the cutout area and then 3 layers at 12, 8 and 4 inches - the outer portion came out amazing - smooth and straight.

The inner portion where we are going to glue the coosa into is going to need work - so question: should I grind the new glass flat or grind the coosa? My thoughts are it will be easier to grind the coosa to match the 2" lip around the transom than to grind the lip - please look at the pics and advise - thanks!

[mshugg]

Great job!  You’re moving in the plus direction now.

You can put a radius at the bottom of your Coosa to get a better fit in the corners.  I’m not sure what’s going on at the top.  If that’s just a random blob of glass, grind it out.  If it’s something like a hull deck seam, I’d stop the Coosa before you het to it.  Your thickened resin will fill some gaps, but you don’t want to use to much.  It’s heavy and adds little in the way of strength.  You also have the option of adding a layer or two of glass to your inner skin to build it out to level.

[RickK]

Looking good.  As mshugg mentioned, round the edges of the coosa that touch all the corners.  You'll also be adding fillets in the corners on top of the new glass to help the coosa fit. Is it only the one side that the 2" lip is interferring? How thick of coosa are you using? You want the core to lay pretty close to the new inside skin. You'll be mixing thickened resin and troweling it on the inside skin, but usually only use a 1/4" notch. Looks like you have more than that in gap. If you grind that lip/hump down from the inside you'll cut through the new glass. If the one lip is the problem, I would agree with you to contour the coosa.  Also before you trowel on the thickened resin, you'll want to scruff all news glass with at least 80 grit.