Great rebuild, just got caught up! Those Kencrafts are big boats for their rated size, should be a beast when you’re done!
you definitely did the right thing by getting the boat blocked up solidly before getting into it. Can’t tell you how much time I’ve wasted because I didn’t have a place I could leave it blocked up.
as far as transom goes, I don’t think the surface has to be perfect, just reasonably flat. Use a lot of thickened resin, apply with a notched trowel. Helps to have holes drilled at intervals in your core so air and excess resin can squeeze out, also gives a good visual indication that it’s pulled down tight to the skin.
I like your idea of trying to match the original structure. I can tell you from experience that messing around with re-engineering the structural stuff is a rabbit hole you don’t want to go down unless you have a lot of time and patience… it’s been an interesting challenge trying to put some science behind my project but one I probably could have lived without.
In your last pic above, while it may have been adequate, that matrix of fibers with voids all through them is the result of a poor layup. Luckily, the voids are not all the way through the laminate. If it was my hull, I’d take some measures to essentially reconstitute/rebuild that layer of your laminate. I’d make some slightly thickened resin (thick enough to stay and lose enough to work easily) and use a trowel or wide putty knife to work the thickened resin into those voids. Work it in different directions to try to work as much air out of those voids as possible. Screed it off smooth and flat in preparation for bedding your transom coring.
If you can time it right, you do the above immediately before bedding the transom. Let the resin applied above begin to setup until it is firm enough to work on top of - maybe a few hours depending temp and catalysation rate. Then, spread more heavily thickened resin (peanut butter) on the face of those repairs and the back of the transom coring. Place and clamp/screw to press any/all air from behind the coring.
While that kind of open matrix in a fiberglass laminate is a sign of poor quality construction, I think it may work to your advantage. If you can work material into those voids and follow that closely with bedding your transom, you’ll get full primary bond between your surface repair and the transom bedding. That surface repair will be ‘keyed’ into those former void spaces keying the new material into the old laminate.
I think… maybe… Kudos on the solid progress.
17’ Henry O Hornet w/ Johnson 88 spl
26’ Palmer Scott project hull
14’ Bentz-Craft w/ Yamaha 25
Wolfie thanks for stopping by! I have read your build thread about 10 times.
PalmerScott I agree about the poor construction and about the “keyed” in effect. I was planning to bed with peanut butter but haven’t thought about doing a thin layer first to ensure a good bond.
Lets talk about transom thickness a little bit. I took three (3) 1/2" sheets of ply with one layer of CSM between them out of the transom. Along with the common theme of this rebuild, replicate the original construction and/or improve upon, I was going to replace with 3 sheets of 3/4" ply leaving the transom plus or minus 2 1/4" then glass . When I was at Lowes looking at the marine ply tonight, three (3) sheets seemed huge in my hand and overkill. At what point is it overkill and Im just adding weight, not strength?
Wolfie thanks for stopping by! I have read your build thread about 10 times.
PalmerScott I agree about the poor construction and about the “keyed” in effect. I was planning to bed with peanut butter but haven’t thought about doing a thin layer first to ensure a good bond.
Lets talk about transom thickness a little bit. I took three (3) 1/2" sheets of ply with one layer of CSM between them out of the transom. Along with the common theme of this rebuild, replicate the original construction and/or improve upon, I was going to replace with 3 sheets of 3/4" ply leaving the transom plus or minus 2 1/4" then glass . When I was at Lowes looking at the marine ply tonight, three (3) sheets seemed huge in my hand and overkill. At what point is it overkill and Im just adding weight, not strength?
hopefully you can pull something useful out of my “learning experiences”… not an expert by any means, but I’ve sure learned a lot from following others before me and screwing up on my own!
I think PalmerScott is spot on with the idea of leveling the skin, looking back I forgot that I did the same thing, then added an extra layer of 1708 to replace the glass I ground off (plus some) and provide an extra tie between the outer skin and the rest of the hull. That might be overkill, but either way gives you a smooth solidly bonded surface to stick the core to.
I think anything more than about 2" total thickness on the transom is diminishing returns unless you’re planning to hang crazy horsepower. I think 2 sheets of 3/4" ply plus decently thick skins (3/16 - 1/4") on each side is plenty. I haven’t done any math to back that up, just observation of the “industry standard” if you will. That’s all most of this era of boats had from the factory, and they lasted 30+ yrs. From wha
Wolfie thats all great information, I appreciate the input. As for the engineering talk, lay it on! I enjoying thinking about it all. I don’t get to use my ME background often, as I work in the construction industry, so its refreshing to hear things like “yield strength”. On the other hand I am not trying to over think things too much. I will find myself down a 3 day worm hole where all I can think about is proper layup and resin/glass ratios and how I can achieve these ratios. Which is why I have been on a week long kick learning how to vacuum infuse the stringers… more to come on that.
The UPS man was nice to me today. Look at that new tank! Moeller 111 gallon tank. I have to say it fits nicely. The best part is I got a great deal on it. There was one left on Amazon and it had free 2 day shipping. You can’t beat that.
I will have to move the front bulkhead forward about 6" when I rebuild them, although I’m not too concerned. The boat came with a 90 gallon fuel tank from the factory, but I received the boat with a wimpy little 52 gallon tank. Everything I have read about these boats as they are bow light so this will help.
And there you have it. Why was your boat designed to be bow light? Was it a poor design or was it to prevent stuffing the bow?
You put a 111 gallon tank( 666 pounds…freaky) that is long. The weight moves to the aft section of the tank as it is used.
Since you’re both Mechanical Engineers, if you place an outboard 3 feet back on a bracket, where does the cob/cog move to…3 feet forward? By moving an outboard up and back from the transom, what are the dynamics of cob/cog changes? Think about that while you’re grinding…and itching.
I don’t have an easy way to compute the COG of the entire boat. But your comment did get me thinking about how much the COG of the tank moved between the three different tanks (52gal,80gal,111gal). Granted this is in an ideal, and level case. The tank most likely isn’t even going to be level while floating still. None the less its an interesting visual. Between the original tank (80gal) and the 111gal tank, the center of gravity moved 4" forward. To me that is not enough to be concerned. Plus the gas is going to be quite dynamic while under way and constantly changing the COG in some way when the tank isn’t slammed full.
Your only adding the weight of an avarage man when it’s full! With 300 hp I would think it would decrese by 20/25 gal an hour at cruse, thats about 140#, wont take long to decrese that weight! Using your trim, i would not think it would be noticed!
Your only adding the weight of an avarage man when it’s full! With 300 hp I would think it would decrese by 20/25 gal an hour at cruse, thats about 140#, wont take long to decrese that weight! Using your trim, i would not think it would be noticed!
Agreed. Man I would love to add a 300hp to the back. I am still debating of what size motor to put on it. It is rated for a 250hp, but over 21’ so not regulated by the coast guard. I just don’t want my insurance company to not fill a claim if anything ever happened because it was over powered. I need to be care with my engine weights in general because in 1988 a 250hp weighed less than the 250hp 4-stroke I would put on it today.
I don’t think this has been mentioned, but to me it look like the origonal transon was cut down to take a 20" shaft! I know I have a 250 hp E tec that weighs 518# on my 23’ and it does well and gets great mileage it replaced a 225 efi merc that got bad mileage, i’m getting 3 time the mileage now. I went to buy a Yamy 4 stroke but its weight and price detured me
I don’t have an easy way to compute the COG of the entire boat. But your comment did get me thinking about how much the COG of the tank moved between the three different tanks (52gal,80gal,111gal). Granted this is in an ideal, and level case. The tank most likely isn’t even going to be level while floating still. None the less its an interesting visual. Between the original tank (80gal) and the 111gal tank, the center of gravity moved 4" forward. To me that is not enough to be concerned. Plus the gas is going to be quite dynamic while under way and constantly changing the COG in some way when the tank isn’t slammed full.
I think you’re on the right track. If you can keep track of changes in the CG and keep it near the original (assuming the original CG was OK) you’re already ahead of a lot of people doing this that have built some bad ass boats by just guesstimating.
I’ve got an excel spreadsheet set up to calculate CG if you’re interested, it’s tooled for my Mako but if you want to try to modify it for your use I’d be happy to share. I weighed every single piece I took out and put back in, along with some educated guesses for hull weight and original CG. Then adjusted tank placement, console placement, even things like deck and stringer materials to keep the CG near the original.
Probably isn’t perfect, but gives me an easy way to really evaluate things like “hey, what if I put the livewell on the transom instead of the leaning post?” or “should I put the batteries in the console or the stern?”. So mdaddy, to answer your question - my CG is moving about 1" forward…
I think the Private Message function still works on this site, if so
Oh and COB I haven’t calculated yet but I will once I finalize my bracket design…
But it won’t change much, probably shift aft a few inches. I’m holding the battery placement as a reserve “ballast” to tweak the balance when everything else is done.
Just thinking out loud and pondering here… what’s the interest in the C of Buoyancy? Seems’ to me, you’re making pretty small changes in the weight distribution in the hull. Move a little gear or batteries or other a little and you can get the CoG very close to original. But, regarding the CoB, I don’t think it’ll matter a lot if the CoB at rest moves a little fore or aft. The risk, from what I can tell, is changing the relationship between the CoG and CoB when planing. CoB will move with the wetted surface and motor/prop lift. It is possible to cause porpoising by having the CoB go to far forward or aft… and the CoB will be moving all over the place when planing.
For instance, when you put a bracket on a hull that originally did not have one or significantly heavier motors, how does one make sure the CoG/CoB relative positions will produce a well mannered hull?
'Seems like voodoo to me.
17’ Henry O Hornet w/ Johnson 88 spl
26’ Palmer Scott project hull
14’ Bentz-Craft w/ Yamaha 25
Just thinking out loud and pondering here… what’s the interest in the C of Buoyancy? Seems’ to me, you’re making pretty small changes in the weight distribution in the hull. Move a little gear or batteries or other a little and you can get the CoG very close to original. But, regarding the CoB, I don’t think it’ll matter a lot if the CoB at rest moves a little fore or aft. The risk, from what I can tell, is changing the relationship between the CoG and CoB when planing. CoB will move with the wetted surface and motor/prop lift. It is possible to cause porpoising by having the CoB go to far forward or aft… and the CoB will be moving all over the place when planing.
For instance, when you put a bracket on a hull that originally did not have one or significantly heavier motors, how does one make sure the CoG/CoB relative positions will produce a well mannered hull?
'Seems like voodoo to me.
17’ Henry O Hornet w/ Johnson 88 spl
26’ Palmer Scott project hull
14’ Bentz-Craft w/ Yamaha 25
you’re right on, the center of buoyancy doesn’t matter as much for planing hulls. Been a while since I studied up on this, but from what I remember when planing it’s the “center of pressure” (which is the equivalent point where all the lift force generated by the planing hull acts) that matters. The relationship between the center of pressure and CG is what determines the behavior of the boat while planing.
From what I remember, porpoising occurs when the CG falls too far aft in relation to the the CP for a given trim angle. The boat will settle out at some angle where the CG is aligned with the CP. When the CG is too far aft, above some speed an instability sets in where when the boat pitches down, the CP moves out of alignmen
Earlier this week I started working on a the transom template. It was more like arts and crafts. Lowes was nice enough to give me two big handfuls of paint sticks, so I glued them all together to get the rough outline of the transom. I knew this wasn’t going to get me close enough to cut the ply so I transferred it to some cardboard. With the cardboard I was able to dial in the template making small adjustments. I taped the cardboard to the ply and cut out the transom. In hindsight I should have cut both pieces of ply at the same time to make sure they were the same, but I just did it separately. I screwed them together and sanded them to the same profile.
Finally something new going in the boat!
I went ahead and did a hot coat on the ply to seal them up. I have to say they turned out great. While the first coat was curing, I whipped up a batch of thickened resin and coated the existing skin of the transom. I left it just thin enough so I could roll it on but it filled the voids nicely. Tomorrow I will get some fiberglass on the new wood and prep to bed them in. Hopefully I can have that done by Tuesday so its fully cured by the weekend and I can fully glass it in.
Might think about how you’re going to terminate the glass at the top of the transom when you’re glassing in the bedded coring. If the plywood coring goes all the way to the top, you’ll round over the front edge and the back edge of the plywood will be lined up with the top edge of the existing outer skin. That means you’ll have to terminate the new glass in a butt joint along that top back edge where the new glass meets the existing outer skin. That will be a weak seam.
Maybe… just thinking out loud…?? lay some glass into the front face of the outer skin while you bed the coring and while wet, lay it over the top of the transom coring and on the the front face? Would need to round over both front and back edges of the coring to allow the glass to lay down. Or, cut the transom coring height down by a few inches to allow the glass on the front of the coring to go up the front face, over the top of the wood, and then up the remaining front face of the outer skin?
I may be way over thinking this… but, if it was my hull… well…
Just trying to think of a decent way to get some glass fiber running from the existing out skin over the top of the coring and onto that front face. Otherwise, that top back seam along the top of the coring is liable to crack. It might not move much. But, without any fiber crossing that boundary, you have very little strength.
17’ Henry O Hornet w/ Johnson 88 spl
26’ Palmer Scott project hull
14’ Bentz-Craft w/ Yamaha 25
Might think about how you’re going to terminate the glass at the top of the transom when you’re glassing in the bedded coring. If the plywood coring goes all the way to the top, you’ll round over the front edge and the back edge of the plywood will be lined up with the top edge of the existing outer skin. That means you’ll have to terminate the new glass in a butt joint along that top back edge where the new glass meets the existing outer skin. That will be a weak seam.
Maybe… just thinking out loud…?? lay some glass into the front face of the outer skin while you bed the coring and while wet, lay it over the top of the transom coring and on the the front face? Would need to round over both front and back edges of the coring to allow the glass to lay down. Or, cut the transom coring height down by a few inches to allow the glass on the front of the coring to go up the front face, over the top of the wood, and then up the remaining front face of the outer skin?
I may be way over thinking this… but, if it was my hull… well…
Just trying to think of a decent way to get some glass fiber running from the existing out skin over the top of the coring and onto that front face. Otherwise, that top back seam along the top of the coring is liable to crack. It might not move much. But, without any fiber crossing that boundary, you have very little strength.
17’ Henry O Hornet w/ Johnson 88 spl
26’ Palmer Scott project hull
14’ Bentz-Craft w/ Yamaha 25
I have been thinking about this. The original transom did not have glass over the top so I have been a bit stumped. I will draw a couple of my ideas up and see what everyone thinks.
So this is what I am thinking as far as glassing in the transom. I am leaning more towards Option #1. My goal is to get the finished product look with the least amount of work. I think I will be able to make Option #1 look better. I will also be able to make a square edge on the outside face.
Sorry I didn’t have any time to do this in CAD for yall. A sloppy hand drawing will have to do.
I like 1. Go ahead and round over the front and back edge of the coring to allow the 1708 to take the shape. That will leave a small V shaped ditch along that top edge just in front of the existing outer skin, but it will be a strong joint/connection. Then, fill that groove with ressin and some shredded CSM. Solid. Clean.
17’ Henry O Hornet w/ Johnson 88 spl
26’ Palmer Scott project hull
14’ Bentz-Craft w/ Yamaha 25
