New boat builder!

I

Ian Booth

New member
I am getting ready to begin a build of a Devlin Black Brandt 3. I have a few questions already that hopefully someone could provide some insight.

First question, do the transom extensions serve a particular purpose? If you moved the transom out to the end of the extension instead of having the recessed motor well will it effect the handle of the boat?

Second question, when scarfing two sheets together the traditional way would be to create an angled scarf. If you changed the scarf to a step cut scarf, would that change the integrity of the scarf. (Reason why I am asking I have a CNC machine that could do step cuts.)

Thanks in advance on the help.
 
Ian Booth said:
I am getting ready to begin a build of a Devlin Black Brandt 3. I have a few questions already that hopefully someone could provide some insight.

First question, do the transom extensions serve a particular purpose? If you moved the transom out to the end of the extension instead of having the recessed motor well will it effect the handle of the boat?

Second question, when scarfing two sheets together the traditional way would be to create an angled scarf. If you changed the scarf to a step cut scarf, would that change the integrity of the scarf. (Reason why I am asking I have a CNC machine that could do step cuts.)

Thanks in advance on the help.
Click to expand...

Ian,
Yes it will have an effect on the hull performance. The hull sponsons in relation to the motor placement also have an effect in the design of the hull. The change in performance and handling will be either positive or negative depending on who you ask. I don't have any personal experience with this hull. I'd suggest calling Devlin for a discussion, it won't the first time he has been asked about this.

As far as the scarf joint, I see no reason it can't be done in multiple steps. I'd suggest several steps (more than just a lap joint) along an 8 degree angle. Using a CNC to cut these steps would be very accurate (assuming the work is held flat during the process) and the steps would actually help in assisting alignment during the glue up.
 
patrick mccarthy said:
Hi Ian
If you have a CNC why not make a dovetail or puzzle joint??
Pat
Click to expand...

Patrick,
For the sake of discussion, my preference would be a scarf type joint. I believe a scarf is the stronger joint while the puzzle joint is preferred for alignment. But that is just my opinion and preference. Once covered in cloth the puzzle joint may be as strong as a scarf joint. During the actual build process, I'd trust a scarf joint more.
 
Dave,

I thought you had a BBIII?

Ian,

I have always been a proponent of the motor well in Devlin's designs, in most cases. The one case I would not want a motor well is if I was going to run a surface drive. In that case I'd omit it for the sake of being able to turn without the shaft hitting the sponsons. With a regular outboard the motor well has some really beneficial attributes. If you get in a decoy line you don't have to hang out over the transom to unfowl. Just raise the motor and lean on a sponson to clear the prop. Much easier. Secondly the ass end of the boat doesn't sag when idling shallow waters. In other words you gain shallow water performance. Another reason it tucks the motor in making it easier to hide. It also reduces the chances of swamping over the transom due to increased buoyancy afforded by moving the motor weight forward and placing flotation aftward of the motor. That makes HUGE difference.

My thoughts on the matter after running them for over 20 years.

Eric
 
Ian~


Regarding the scarf (or scarph for us Old School types) joint for joining sheet plywood: I would lean toward the scarph over any sort of stepped or lap joint. I would readily defer to a mechanical engineer, but intuition (and experience) tells me that the scarph distributes the stresses more evenly and avoids creating any weak spots - or hard spots when bent.


Scarphs are easy enough to cut with an electric plane + belt sander. 1:8 is traditional for sheathing and 1:12 for things like spars and longitudinals.


You could also cut your scarphs with a straight bit in your router and a jig built with a 1:8 slope.


All that said, it may very well be that any other the other joint types mentioned would prove sufficient once slathered with thickened epoxy and sheathed both sides with 'glass and supported by framing. So, my opinion may be purely academic.


In any event, I look forward to following your build!



All the best,


SJS





 
Eric Patterson said:
Dave,

I thought you had a BBIII?

Ian,

I have always been a proponent of the motor well in Devlin's designs, in most cases. The one case I would not want a motor well is if I was going to run a surface drive. In that case I'd omit it for the sake of being able to turn without the shaft hitting the sponsons. With a regular outboard the motor well has some really beneficial attributes. If you get in a decoy line you don't have to hang out over the transom to unfowl. Just raise the motor and lean on a sponson to clear the prop. Much easier. Secondly the ass end of the boat doesn't sag when idling shallow waters. In other words you gain shallow water performance. Another reason it tucks the motor in making it easier to hide. It also reduces the chances of swamping over the transom due to increased buoyancy afforded by moving the motor weight forward and placing flotation aftward of the motor. That makes HUGE difference.

My thoughts on the matter after running them for over 20 years.

Eric
Click to expand...

Eric,
Yes you are correct I do have a BBIII. My fingers did not type everything my mind was thinking. The sentence should have read; I don't have any personal experience with this hull modification of eliminating the motor well.

Ian,
It would serve you well to do a search within this site, for threads on the BBIII and modifications to it's design. When I get a few minutes I'll send you a link or two of very pertinent changes which most everyone has incorporated into their build either during or post build. Two things come immediately to mind (a) trimming inside corners of the motor well for increased motor clearance in shallow water position (b) addition of a splash guard around the inside perimeter of the motor well. If you like, send me a private message with your phone number and we can chat.
 
Ian Booth said:
I am getting ready to begin a build of a Devlin Black Brandt 3. I have a few questions already that hopefully someone could provide some insight.

First question, do the transom extensions serve a particular purpose? If you moved the transom out to the end of the extension instead of having the recessed motor well will it effect the handle of the boat?

Second question, when scarfing two sheets together the traditional way would be to create an angled scarf. If you changed the scarf to a step cut scarf, would that change the integrity of the scarf. (Reason why I am asking I have a CNC machine that could do step cuts.)

Thanks in advance on the help.
Click to expand...

You'll like having the sponsons.

Go for the scarf, they're easy and work fantastic!!
 
Hi Ian,
And welcome to boat building. I think you'll like having sponsons for the reason's mentioned. Spent a lot of time laying across mine digging long lines and decoy anchors out of the prop..... If you need the room, why not build a bigger boat? Definitely would not try to skimp on the scarf angle; believe that affects strength. Just use a cheap power planer or coarse belt/disc sander to grind it down.

v/r
Bill





View attachment DSCN1863.JPGView attachment DSCN1350.JPGView attachment image0004.jpgView attachment DSCN1176.JPGView attachment IMG_0316.JPG
 
Local bayman here builds his own sharpie. Helped him many years ago, he did a 10' scarf that fell between the ribs. He backed it up with 3/8" plate of plywood as he put large cleats for his scallop dredges. He used AC plywood and galvanized screws, glass on the outside and deck. Boat still going after 30 years with daily use.
Now all the baymen are using Carolina skiffs.
 
Ian,
Reread your post and realize now you were talking about a step cut scarf. Not sure what that is, so I cannot comment on that. Devlin sells kits with a jigsaw type connection cut with a CNC; you might email his shop to see their thoughts or recommended connection type since you have the good tools.

v/r
Bill
 
Bill Burruss said:
Ian,
Reread your post and realize now you were talking about a step cut scarf. Not sure what that is, so I cannot comment on that. Devlin sells kits with a jigsaw type connection cut with a CNC; you might email his shop to see their thoughts or recommended connection type since you have the good tools.

v/r
Bill
Click to expand...

Bill,

Just speaking from my background but this what I envisioned when Ian says he wants to cut steps using his CNC to create a scarf joint. The drawing is not to scale and does not show nearly as many steps as what may be cut. The smaller the steps the smoother the surface finish along the 8 degree slope. Most "profile milling" uses the same technic, a series of steps creating a rough profile, followed by a ball nosed endmill in even finer steps to finish the surface.

Given enough steps, it would become just a series of parallel ridges along the surface.

Ian may have something else in mind but that's how I took what he wrote.





View attachment scarf.jpg
 
Dave

If I was handed that in a matter of a few minutes I could take my hand plane and make a traditional scarf. I don't see any advantage to the steps. Not saying one doesn't exists, but I'll stick with the 8:1 scarf that is well proven.

Eric
 
Dave,
Looking at your picture, I am having flashbacks to programming a handheld calculator (HP 15c) to do a "step" integration by calculating a series of very small rectangular areas under a curve and adding them up. The smaller the rectangles, the more accurate the results. Argg! No sleep tonight!!

Agree with Eric, think I at that point I would just knock the corners off with a plane or sander for a nice, smooth, 1:8 slope.
 
Hi All
I learning some good stuff here.
But I do have a question.
Is the idea of scarf cut to create a large surface area for the glue bond?
And if yes wouldn?t the stepped one have more surface area?
Pat
 
Ian,

Here are a couple photos which show some of the changes I made on my BBIII. (Clicking on the photos will expand them for better viewing)

Similar to what you can see in Bill's photos, I also added a splashguard in the motor well. This photo is the initial fit up before glassing it in. Also note the sharp pointed bottom corners of the rear of the hull. These will be trimmed later.


View attachment 20180319_130100.jpg


And as trimmed for shallow water drive. This was of course, later cleaned up, glassed and repainted.


View attachment after corner trim.jpg

In this photo and in the above photo, you can see the rear edge of the cockpit and the upper edge of the transom for the motor.

View attachment 20180516_172109.jpg


I added a piece to wrap the cockpit cowling all the way around the rear edge and extend the cowling as close to the motor as feasible. This keeps water on the read deck from draining directly into the cockpit.


View attachment 20180516_172127.jpg


Please note; You will see a splash guard in some of the photos which show metal clips holding it in place. This was only a temporary proto type, which was later replaced with marine plywood and glassed in place.


The photo below is looking upward at the bottom of the hull. To solve some propoising issues, I built up a small wedge under the trailing edge of the hull. Some guys will glass on wood wedges, I chose to use thickened epoxy to build up the wedge. You can also see where the previously trimmed corner has now been glassed and the underside of the permanent splash guard.


View attachment forms-removed.jpg




View attachment 20180627_094223.jpg
 
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Bill Burruss said:
Dave,
Looking at your picture, I am having flashbacks to programming a handheld calculator (HP 15c) to do a "step" integration by calculating a series of very small rectangular areas under a curve and adding them up. The smaller the rectangles, the more accurate the results. Argg! No sleep tonight!!

Agree with Eric, think I at that point I would just knock the corners off with a plane or sander for a nice, smooth, 1:8 slope.
Click to expand...

Bill and Eric
Ahh yes but then you miss the joys of sitting there watching the CNC run multiple perfectly straight cuts across the piece. Rest assured that enough steps can be programmed that it will be smoother than the scratches left from your guys belts sanders or power planes. hehe [w00t]
 
patrick mccarthy said:
Hi All
I learning some good stuff here.
But I do have a question.
Is the idea of scarf cut to create a large surface area for the glue bond?
And if yes wouldn?t the stepped one have more surface area?
Pat
Click to expand...

The idea is to gently spread any forces on the joint over a large area and to minimize end grain gluing which is weak. Hard corners and edges can be a location for forces to accumulate and cause failure. Not sure if the stepped joint in this discussion falls into that category but it certainly has more end grain contact and for that reason I'm now on the side of the good old 8:1 scarf as being superior over the stepped joint.

Eric
 
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Eric Patterson said:
patrick mccarthy said:
Hi All
I learning some good stuff here.
But I do have a question.
Is the idea of scarf cut to create a large surface area for the glue bond?
And if yes wouldn?t the stepped one have more surface area?
Pat
Click to expand...

The idea is to gently spread any forces on the joint over a large area and to minimize end grain gluing which is weak. Hard corners and edges can be a location for forces to accumulate and cause failure. Not sure if the stepped joint in this discussion falls into that category but it certainly has more end grain contact and for that reason I'm now on the side of the good old 8:1 scarf as being superior over the stepped joint.

Eric
Click to expand...

Eric,
You are missing the point that the drawing only is a rough sketch. The step would be very small as in the actual step would be nothing more than surface roughness. There might be 100 steps in a 1/2 inch thickness.
 
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