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Polymerman Boat Build: Temptress
Quote from Bob Kody on 26th February 2024, 4:39 pmHi Dan – Do you have an estimate of the weight of Temptress? I am adding support structure to the strongback, as I do not think the MDF strongback legs are enough.
Get three questions(not urgent):
1) How much will temptress weigh (just the wood epoxy structure, excluding the engine, etc)?
2) what will the total weight be when Temptress is running in the water?
3) What is the weight of each stringer?
Thanks,
Bob
Hi Bob
I have a total finished weight for Temptress based on the Ilmor driveline, which is 4000lbs or 1814kgs. Regarding weights of individual components though I am not really sure. I haven't got my CAD model set up to accurately spit these out right now. This is something Michel should have recorded though so I'll ask him.
Cheers
Dan
Bob:
In watching your video's, I noted that you are using sapele remember it is 25% heavier than Mahogany. I was considering using that also but that would increase the boat weight to about 5000 lbs. changing the performance numbers. Though I really liked the color over the African Mahagony.
I was watch watching a interesting You Tube video last night. https://www.youtube.com/watch?v=3k7V9tIKg9I&list=PLrosrqPggtqCAd9W_WSGdxqgMM_PgCciH&index=29&t=609s
They use a solution of Potassium Dichromate dissolved in water really works great. The only thing is Potassium Dichromate in crystal form is kind of bad stuff. I don't know if it's safer in solution. The guy says you can even get it from Amazon. They have it in solution form but when you do a search on Amazon it defaults the crystal form to Sodium Dichromate. My old chemistry days have been too long ago to know if you can use the Sodium. I would love to talk to you directly. My number is 248-410-9684.
Greg Koukoudian
Thanks Dan and Greg. Flipping this boat will be a significant engineering challenge.
Greg - I will call you, or feel free to call me +1 651 231 8544
Quote from Gregory Koukoudian on 2nd March 2024, 6:27 pmBob:
In watching your video’s, I noted that you are using sapele remember it is 25% heavier than Mahogany. I was considering using that also but that would increase the boat weight to about 5000 lbs. changing the performance numbers. Though I really liked the color over the African Mahagony.
I was watch watching a interesting You Tube video last night. https://www.youtube.com/watch?v=3k7V9tIKg9I&list=PLrosrqPggtqCAd9W_WSGdxqgMM_PgCciH&index=29&t=609s
They use a solution of Potassium Dichromate dissolved in water really works great. The only thing is Potassium Dichromate in crystal form is kind of bad stuff. I don’t know if it’s safer in solution. The guy says you can even get it from Amazon. They have it in solution form but when you do a search on Amazon it defaults the crystal form to Sodium Dichromate. My old chemistry days have been too long ago to know if you can use the Sodium. I would love to talk to you directly. My number is 248-410-9684.
Greg Koukoudian
Bear in mind that the 4000lbs is the boat all in including mechanical so I wouldn't think you'd quite be at 5000lbs but yes, piling on a bit more weight with Sapele.
Another thought here on weight for you guys to consider, although I haven't said so elsewhere yet, I'm planning to get my Temptress build underway shortly... yes a proper sized one!
Therefore I am looking into costings/weights and deciding upon timbers in a more serious note. We can get African mahogany here but it's very costly so I'm going to run with Sapele or possibly it's nicer cousin Utile for framing and stringers. Planking species however can offer significant weight saving that will offset the additional weight of these Sapele type mahoganies. I am almost certainly going to plank the boats internal layers with Cedar, at the inch thick bottom that's on this boat that's a lot of timber and weight saving potential!
Also I'll likely do the longitudinal battens in something like larch or spruce. With Sapele/Utile only making up major framing I wouldn't think the weight will be much different.
Very interesting. Thanks for the insights Dan.
Your timing is perfect. While I have made the frames, stringers and keel out of Sapele, I plan to is either Utile, African Mahogany or Philippine Mahogany. I have some research to do.
Bob
Question: Chine positioning on Stem
See the attached photo. The 3D model shows the change in profile of the Stem being 1/4″ below that bottom of the Chine Laminate bottom surface. Is this correct? Or should the bottom of the China Laminate align to the change in the Stem Profile?
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That I believe is because there is still another layer to go on the chine flat. 1x layer of hull planking will face the plywood chine flats. I would recommend installing this once the bottom planking is finished as it will allow you to neaten up the inner edge of the chine run that may otherwise end up a little wayward, it certainly did on my model. This additional layer will take this place of this "tab" though so it will eventually be cut away. It is helpful to reference the chine landing position for now though.
That should equate to the difference there so yes you want to install the chine as positioned in the screen shot. Is the additional chine planking layer in your model? It may be under the bottom planking component.
Can you ghost out the stem in your CAD software? If so you should be able to view the chine landing cutout as below:
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Thank you, Dan. I am pretty sure I understand. But we will all find out together when I publish the video 🤣
Chine Top Rail Question:
With Temptress the chine top rail cross section is 1 9/16” x 1 9/16”. These boards need to be bent and twisted to match the curves of Temptress. I have found this very difficult to do.
I feel that one large square beam will hold the shape and make for a smooth curve. I just cannot bend and twist this large beam.
So should I steam the beams? Or I have cut the beams lengthwise, and this solved the problem. See attached…. The lengthwise groves allow the beam to twist and bend, and keep the square cross-section. I will need to fill the groves with epoxy later… but at least I won’t have water captured in the wood.
Please advise if I should steam or use my lengthwise cut beams.
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Ideally these timers should be laminated out of smaller sections. I wouldn’t really recommend steaming and using larger cross sections for any of the timbers in Temptress. Although it may help to make the curve, you can end up with a segmented bend as it forms around the hard spots created by the frames. Larger timber sections are also not very dimensionally stable.
As per the Gougeon brothers practice, we don’t want any single timber to have its smallest dimension greater than 25mm/1″, anything above that should be into lamination territory.
If the curve doesn’t have too much edge set then you can do it out of wide and thin layers. For example 1-9/16″ x 1/2″ layers. If it has to bend in two directions then it will need to be quartered as I did when I installed the sheer clamp in the model.
To get a nicely laid, fair curve you want to use the largest timber possible that will comfortably land and form a fair curve and or twist. If you go too small with sections then you will get a very unfair curve that will be difficult to manage.
I wouldn’t recommend just cutting into the timber as you have above, even if you try to fill those channels with epoxy it will be very difficult to do thoroughly and that will create a serious potential rot trap down the line. The better move would be to fully section that timber and lay the 4 parts individually. Once you’ve got the inner timber glued up and fair, the remaining ones that fit alongside it will lay very easily. Focus on getting the first one fair though.
The chine top rail may well lay as 2-3 wide thin strips, the sheer clamp though will definitely need to be quartered as there is a significant bend, twist and edge set in it.
Hope that all makes sense.
This makes sense. Extra work, but makes sense.
Thank you.
Bob
I am ready to router out the limber holes in Temptress. What size slots should I cut on the frames. Please tell me the depth and width.
Thank you.
Bob
I'd aim for something like this Bob, use around about a 30mm or 1-1/4" ball nose router bit. Then square off the little return up against the keel and stringer with a chisel so you've got a nice neat arch. Circa 30mm wide of course and 15-20mm deep, soften the edges with sand paper and seal WELL with epoxy before the bottom planking goes on. I'd do this after you have faired the framing so that fairing doesn't affect the size of the final hole.
A very old video of me doing this on Miss Isle: https://www.youtube.com/watch?v=HdwPZKKxDkc
I would personally do this for all frames except frame 9. It would be a good idea to split the bilges to a fwd and aft area so that any cockpit water doesn't unnecessarily transfer into the engine bay and also any potential oil, fuel or water leaks (not that you should have any) transfer into the cockpit.
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Thanks Dan. As usual, a thorough answer.
Greatly appreciated.
Bob
Fellow Temptress Builders – I built my jig and am routing the Limber Holes. See photo.
Jig works well from Frame 4 to 13; I am not cutting holes in frame 9.
However at the front of the boat, the curve front-to-back and the steep angle from center-to-sides make this difficult. Any advice?
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You might need to do them manually in this area Bob. Cut a series of slots cut with a hand saw, and break out the bulk of the material with a chisel. You could then use a round rasp file to neaten up the bottom of the slot.
Thanks Dan. Sounds like a challenge…. I ordered a compact router with a tilt base. If successful, it will be in my October 12th video.
If not, I will follow your advice Dan.
PS – Wait till you see how I spile the planks….
What is M? Is this something I add before planking the bottom?
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These are the stringer clamps, their location is itemised on each of the frame drawings and you should also be able to reference them in the 3D model. They give a reinforcement of the stringer to frame bond and help to transfer the engine thrust through into the boats framing.
They could be installed at any time almost, just consider that they may have an effect on your limber holes.
I wanted to post some photos today, as I am very proud for completing the topside battens today! 180 notches (including the stem, frames and transom) and 12 battens. I am getting better at scarf joints...
Best wishes to other Temptress builders.
Bob
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