TW28 Scantlings

[Rum Runner]

Hi,

I have the plans for the TW28 and I have had the privilege of meeting Rick and seeing the hard work he has put into his TW28 build. I am interested in increasing the size by the 10% max, as stated by Jacques. I have read through the other posts and understand that all dimensions need to be increased by 10%.

I just want to verify, if this also means the plywood thickness for planking and bulkheads needs to be increased? Beam sizing? Any other scantlings that need to be considered?

Before making such a large commitment, I want to make sure I understand all that is involved in the 10% increase, as I have not seen any posts on here of builders who have increased to 10%, except for Rick's.

[fallguy1000]

Generally NO to beams and planking. Generally no to most any major structural change. Typically, boats are specified with significant safety margins that allow for modest modification without major changes.

That said, the designer is the best person to answer.

A boat that is 9' beam extended 10" may encounter some structural deficit in deck spans, for example, which may be specified closer. It would be unfair to expect the designer to catch all these subtleties, but a 10" increase is typically a rather major span change and you will want to watch for these. They are manageable, but must be watched for...by you, diring the build.

If you encounter span issues; there are a multitude of means to manage.

[BarraMan]

As a fan of the 10% up-scale I feel a need to reply to this post!

Let me make a couple of points!
1) Up-scaling an already big boat produces a very BIG boat! Mine went from 20' to 22', with a corresponding increase in beam and height. The required increase in build marterial (ply, glass and epoxy) is significant - with a corresponding increase in cost. That said, if I was to build a TW28, I would most likely up-scale it!

2) Jacques is the best person to answer your question about ply size. In the case of my hull, from the Mangusta 20, he recommended additional layers of glass only. My boat is capable of quite high speeds, which would not be a factor with the TW28, but there may be other structural issues.

I will watch with interest for this build to proceed!

[TomW1]

Normally and why the limit is 10% is so Jacques does not have to redesign the boat. Once you reach that 10% limit lever pressures on the hull from the water pushing starts to increase above what the current design allows. Jacques will see this soon I would think. If you don't go over 10% you should be fine, maybe an extra layer glass on the bottom, but with a displacement boat like this you may not need one. Wait for Jacques to replay.

Tom

[OneWayTraffic]

At a 10% upscale displacement boats will displace significantly more water. Extra ballast might be required to bring her down to her lines. If this is the case, no harm in beefing up the structure here or there in terms of performance, if not cost.

Definitely a question for the designer.

[fallguy1000]

At a 10% upscale displacement boats will displace significantly more water. Extra ballast might be required to bring her down to her lines. If this is the case, no harm in beefing up the structure here or there in terms of performance, if not cost.

Definitely a question for the designer.

I wish my boat had that issue. A bigger boat also weighs more. If he has to use shot bags; he'd be really lucky.

I encourage everyone to build as light as possible.

[Rum Runner]

Thanks for the feedback. One of the reasons I am very interested in the TW28 is the wealth of knowledge and experience on this forum.

Stretching 10% would provide just the right amount of accommodation and storage for long term cruising. Within our needs and resources.

Hoping Jacques will comment when able.

Here is a layout we would like to accomplish. 10% increase, with long pilothouse version. still leaves a decent sized cockpit.

[Rum Runner]

How can I bump this thread so hopefully Jacques will answer my questions?

[jacquesmm]

It looks very good, I am surprised how muhc room you created and used.
I have to check if al that will fit in 3D. I can't do that know: I am on the road (camping) and will be back begin November.

[Rum Runner]

It looks very good, I am surprised how muhc room you created and used.
I have to check if al that will fit in 3D. I can't do that know: I am on the road (camping) and will be back begin November.

Thanks for responding Jacques. Can you please look at my original post. I am trying to assess what all is involved in doing a 10% increase. I understand all the dimensions will have to be recalculated, nesting re worked, but I am uncertain if plywood thickness needs to increase or what other scantlings need to be reconsidered.