Aluminum 25' skiff

I am new to boatbuilding but am investigating this due to the complete lack of quality boats offered commercially. I live on the east coast where aluminum boat builders are very rare, and used aluminum hulls unheard of.

I need a 25ftx 8ft skiff type hull with a 5ft bow depth, closed 10 to 14* transom, and pleanty of freeboard. Looking to keep it lightweight with 1/" transom, 3/16" sides/bottom 5025 construction.

I am considering taking a design and finding a cutter then doing the welding myself.

One question I have is say a typical design for a 25ft boat, would there be pieces that weigh more than say 150 lbs? What would you do in the situation? How do you handle the big pieces for the bottom and sides if they are too heavy to pick up?

 

You will have to handle (in all probability) some pieces that are over 150 lbs. In our shop we use three guys and a winch attached to the cieling. And it's not so much the lifting, but he holding of things in place at just the right angle while it gets tacked in place that is the pain in the neck.

 

by the way, it's a no-no around here to lift more than 60lbs without another helper.

 

I have a design for a boat that fits your description. Several have been built to date using computer-guided plasma-cut panels that were trucked to the builder's shop for fabrication. These are commercial boats used primarily in the local fishing industry. Contact me at the e-mail address in my profile if you are interested.

 

Not seeing the the design of your boat it's hard to tell but I would say that you will have a few parts that will push or exceed 150 lbs. A 25'x36"x3/16" sheet of 5052 weighs about 165 lbs. so certainly each side would be 100 lbs. or better. Incidently, you may already know this but an easy formula for weight of aluminum is- Lenght x width x thickness x .097 = lbs. (.097 being the density of 5052 other alloys such as 6061 vary slightly but not enough to really matter)
I am thinking typo, but if not, are you really thinking of 1" plate for the transom? If so, that would put the weight of the transom alone at over 300 lbs. I would recommend 1/4" ( im guessing that is what you meant I see a lot of "underthick" transoms out there and I just dont get it. The amount of strength gained by using 3/16 instead of 1/8 for example, is well worth the relatively small increase in cost.
Another thing I can tell you, and I have first hand experience with this, if at all possible, do not go with 5052 for your bottom plate! Step up to 5086. In fact, if you can, use 5086 for the sides and transom as well. The pounding on the bottom of a 25' craft is just too much on 5052 and it WILL fail eventually. It can and has been used succesfully, but in my experience the amount of extra reinforcment it requires not to mention the extra labor involved to put in that reinforcment far exceeds the small cost to upgrade to a better alloy. I think it was Reynolds or maybe Alcoa(cant remember anyway one of the major aluminum mfgrs ) put a 1/4" plate of 5086 into puget sound to test the effects of the salt water. After 30 YEARS!!!! they took it out because nothing was happening! Thats what I want on the bottom of my boat! 5052 would be ok to use on the sides if cost is a factor. Transom too, but I would really try to use 5086. Dont get me wrong, 5052 is a high grade marine alloy and an excellent all around choice, (90% of the metal I use is 5052) I just dont feel its strong enough for the high stresses put on a bottom.
You may consider using .160 for the sides instead of 3/16" save a little weight with no real disadvantage. I have used and seen used .160 sides with .190 bottom to excellent results. Your preference.
Definately do not lift more than 50 or 60 lbs by yourself. My hat is off to thunderhead19 for throwing out some safety advice. It may seem pointless to ask another person for help lifting a 60 or 80 lb sheet of metal, but trust me, It is the thing to do.
As far as handling of heavy pieces, you have two choices. Heavy equipment such as hoists or maybe a forklift. Or my favorite, Manpower! Call in the neighbors! Just be sure you have more than enough people to do the job. As thunderhead19 said, its the placement of the pieces that is the hard part. You will need at least two people and yourself to get a 25' side into a slotted extrusion and tacked.I would use a couple more than that. Assuming you are using a slotted chine extrusion. If not, tacking plate edge to edge will require more help. Ling up a 1/4" transom and tacking it in is not a one man job either. But once you get the hull together you should be able to do most of the rest by yourself with only occasional calls for help.
Hope this helps( Feel free to email me with any questions)
Joey

 

Greatly appreciate the advice and yes that was a typo it should have read 1/4" transom. Suprised about the 5025, My current boat is a 1961 5025 23 footer. It has been abused and the 5025 is in excellent condition, I always thought that 5025 weathered better as far as not becoming brittle. This boat has been in saltwater all it life, previous owner did't use a zinc!

I am mainly looking at building my own because there are no local builders building what I need, the closest builder with a design I like is in Newfoundland and I'm in Pennsylvania.

I can handle the welding and cutting, the lifting is my concern. I may end up driving to Newfoundland.

 

My mistake Regal,
Just glancing at your post I saw 5052, not 5025. And that is what I had based my opinions on. However, I cant find any information on a 5025 alloy. Anywhere. Gregor boats claims they use 5025 on their boats, but I'm not sure if thats a typo or not. I'm Not saying it doesnt exist, just that I've never heard of it. My Pacific Metals aluminum mill products specifications book makes no mention of this alloy.
As I mentioned in my reply, 5052 can and has been used with good results for bottom applications. Also one thing I didnt mention is that you can get 5052 sheet in different hardnesses. h- 32 h-34 h-36. I have found the difference between h 32 and h 34 to be substantial, so if you use 5052 get it in a harder sheet. I have no experience with h 36.
My former employer went to 5052 H-32 bottoms on a new entry level boat to cut costs. These were 15' to 19' boats. The result? Recall. And hundreds of warranty repairs.(Take a guess on who repaired a good percentage of them.) They switched to 5086 (as is used on all of their other models) and guess what? Field failures all but dissappeared.
So if you use it, get in in h34 0r h36, reinforce it well and you should have no problems. Just my own opinion based on my experiences with it. Above all else, have fun with your project!

If anyone out there has used a 5025 alloy, please share your experience. I would be interested to learn more about it.
Joey

 

Sorry again, I have been typo crazing lately, 5052-H32 was what I was refering to but being from 1961 it was probably better than the 5052 the mills are producing now.

 

No problem, I'm the typo king!!

The fact that your vessle is still sound is a testament to excellent materials in 1961, and/or a very knowledgable builder. What make is it?

 

It is an old lonestar, but solid and has held up to over 40 years of the chesepeake bay. I need to build something this size but with more deadrise, it is only 5* at the transom