Sailboat building and hull worthiness myths

[goboatingnow]

XPS is a structural foam , round here you can build concrete walls on top of the stuff, various option up to about 700 Kpsa compression strength

[Chotu]

Originally Posted by goboatingnow

XPS is a structural foam , round here you can build concrete walls on top of the stuff, various option up to about 700 Kpsa compression strength

This is absolutely true. It’s also waterproof. It’s great stuff. But there’s a little bit of a difference between that and the structural foam we use on boats.

First, it’s friable. It can’t take continued flexing inside a composite panel. It’ll fall apart. It’s fine for stationary things but in a vehicle subject to millions of stress cycles, it’ll fall apart.

Second, there is the compressive strength. It maxes out at 700Kpa as you mentioned.

A middle of the road compression strength for a structural foam suitable for building boats is 1,500Kpa or over twice the compressive strength of xps. Boat building foam is available with compressive strengths up to 4,400Kpa. More than 6 times the compressive strength of the maximum xps varieties.

Basically, build a shelf out of it. Build interior cabinetry or furniture. Build things on land from it. But do not ever use it for a hull or structural bulkheads or anything else structural in a vehicle such as a boat or plane or car. It will fall apart. And/or fail by crushing.

I’ve used it for some non structural things like shelving. I’m considering using it for a non structural bulkhead too. Works great in applications where it’s not subject to high loading or continuous flexing. Just don’t build a boat from it.

[mako]

Originally Posted by psk125

You might enjoy the Gougeon brothers' book on yacht construction. They go into some detail about various layers and strengths of different materials in hulls and other structures.

I remember as a freshman Wolverine studying naval architecture, 1984, the Gougeons came and gave a presentation on that crazy new system of theirs.

Very interesting and compelling. For recreational vessels it certainly offered advantages over wood or molded fiberglass.

[raahell]

Doing the research and gaining an understanding of what comprises boat strength and the different ways that manufacturers achieve it is a great first step but you should be careful NOT to overemphasize this single characteristic. A successful sailboat design balances strength (in its many forms) to weight but also achieves a balance in stiffness, righting moment, seakindliness, upwind, off wind and down wind performance, interior volume, exterior comfort and safety, etc, etc. Read up on those as much if not more than your research on "strength" to gain a balanced understanding of what makes a successful sailboat.

Even better (if you haven't already) get out there and sail in a variety of boats, either by joining a local racing/sailing club and offering yourself as crew, or pay for one or more wet charters. Don't buy a boat until you know for sure that this is something you really want to do and are suited for.

The primary question you should be asking yourself is "what type(s) of sailing do I want to do with the vessel?" The answer to this question will then lead you down the road to finding a matching sailboat type. Having narrowed down to a short list of manufacturers/building construction/material choice methods, remember that there will be differences in quality from boat to boat, due to irregularities and changes made in construction and material choices throughout the boat's production series. Many boat types have user groups online that have a wealth of information about this. They are very open about strengths, flaws, useful mods, etc. These forums are well worth taking the time to join in order to profit from owners' real life experiences.

Since you are looking to buy a used vessel, the ravages of time will have given you hints on how well any particular boat has stood up to the demands of being used and abused. It is thus up to you and your surveyor to find the hints that will tell you whether a boat is worth investing in.

My humble advice is to start looking at real boats right now - even if you're not looking to purchase at this time. Take an experienced boat owner with you - preferably one that has experience in maintenance and repairs in the boat construction/materials that you have narrowed down to. Get him/her to show you what to look for in your pre-survey, how to recognize good from poor construction techniques, how to recognize corrosion, delamination and other types of degradation, how to recognize and judge the quality of modifications and prior repairs. Armed with this knowledge, you will be much more able to separate the good from the bad once you are truly ready to become a sailboat owner.

My final point: As any boat owner will confirm, the degree and competency of care by prior owners has as much impact on a given boat's longevity and reliability than the original design and build quality.

[Colin A]

Ypu can pick up the book elements of boat strength by Gerr as a decent starting point.

I was trained as a boatbuilder and worked in boat yards and investigated claims for yacht insurance. I have always been amazed at how badly you can build a boat and have it not sink. Workmanship also matters alot more then gets talked about. It's fully possible to build an awful boat from good materials.



There are things I prefer in construction of a boat, but I don't outright write off other ways of doing it. There also is a matter of use case. For instance my little 16' powerboat is a good example of not so great boat construction, but for buzzing around lakes and rivers and doesn't matter much (although it does mean more repairs then a well built boat)

[LargeMarge]

Referencing the video at Post One:

Buffoonery.

*****

For comparison, during the 1970s and 80s, I trained with Andy Ahpo and Dong Tri.

During examples of our potential, Mister Ahpo stood across the room from a man-size coat-rack holding several burning candles at different levels.
Responding to requests up-and-down left-to-right, he caused one candle-flame to flicker while adjacent flames -- inches away -- remained stable.... over and over for each candle on display.

Mister Tri bent straight rebar into a circle by stroking the air inches away from the steel.

Each ridiculed the stacked-brick demonstration.
Each could pulverize a specific brick in the stack... while leaving its neighbors intact.

*****

For a half-century of boating, each if our builds was aluminum.
Each is still floating despite all manner of unintentional destructive testing.

[barnakiel]

Originally Posted by Notyetsinking

Hi,


(...)



However, one thing I have continually come across is the myth of hull thickness corresponding to the boats strength



(...)


I am a young engineer,



(...)

Hi,


I am an old sailor.


I can tell you this : all other things equal, a 12 mm handlaid laminate is stronger (more impact resistant, less flexible, etc.) than a 6 mm handlaid laminate.


Proven empirically, by hacking into boats old and new.



Does this stand against any formulas a young engineer knows?


Then PLS let me read those formulas. Perhaps my hull is too thick at 6 mm. Perhaps what I really want is a 0.6 mm hull.

[Buzzman]

Originally Posted by rbk

eXpanded PolyStyrene foam

Actually this is not correct.

EPS = Expanded PolyStyrene Foam

XPS = EXtruded PolyStyrene Foam.

EPS is the stuff made from tiny balls of foam that is 'blown' under heat and pressure into a mould. Its the stuff large baulks of 'industrial grade' foam are made from.

XPS is the process by which Corecell and similar boat-building and modelling foams are made, extruded from a die in a 'continuous extrusion' method that produces a very fine air bubble and closed cell foam.

This is an important difference

[Franziska]

This. Chotu is correct.

In the boat building industry there are much better cores than XPS.

Standart boat building foam cores are made of closed cell non crosslinked PVC (like Divinycell or Airex) and SAN foams (like Core Cell).

Both types are tougher and less brittle than EPS and XPS.
XPS & EPS have a history of failing when exposed to many heavy load cycles.

For more on this, you can read here:

https://www.boatdesign.net/threads/c...-linked.42009/

You'll find Eric Sponberg in the list of contributers. He's a great guy with a long successful career of yacht design behind him.

Originally Posted by Chotu

This is absolutely true. It’s also waterproof. It’s great stuff. But there’s a little bit of a difference between that and the structural foam we use on boats.

First, it’s friable. It can’t take continued flexing inside a composite panel. It’ll fall apart. It’s fine for stationary things but in a vehicle subject to millions of stress cycles, it’ll fall apart.

Second, there is the compressive strength. It maxes out at 700Kpa as you mentioned.

A middle of the road compression strength for a structural foam suitable for building boats is 1,500Kpa or over twice the compressive strength of xps. Boat building foam is available with compressive strengths up to 4,400Kpa. More than 6 times the compressive strength of the maximum xps varieties.

Basically, build a shelf out of it. Build interior cabinetry or furniture. Build things on land from it. But do not ever use it for a hull or structural bulkheads or anything else structural in a vehicle such as a boat or plane or car. It will fall apart. And/or fail by crushing.

I’ve used it for some non structural things like shelving. I’m considering using it for a non structural bulkhead too. Works great in applications where it’s not subject to high loading or continuous flexing. Just don’t build a boat from it.

[Chotu]

Originally Posted by Buzzman

Actually this is not correct.

EPS = Expanded PolyStyrene Foam

XPS = EXtruded PolyStyrene Foam.

EPS is the stuff made from tiny balls of foam that is 'blown' under heat and pressure into a mould. Its the stuff large baulks of 'industrial grade' foam are made from.

XPS is the process by which Corecell and similar boat-building and modelling foams are made, extruded from a die in a 'continuous extrusion' method that produces a very fine air bubble and closed cell foam.

This is an important difference

A little add on for clarity.

EPS = Expanded PolyStyrene Foam

XPS = EXtruded PolyStyrene Foam.

EPS is the stuff made from tiny balls of foam that is 'blown' under heat and pressure into a mould. Its the stuff large baulks of 'industrial grade' foam are made from

. -absolutely correct

XPS is the process by which Corecell and similar boat-building and modelling foams are made, extruded from a die in a 'continuous extrusion' method that produces a very fine air bubble and closed cell foam.”

-Small distinction is that XPS isn’t a process, it’s a material. The X is the process, the PS is the material. X stands for extrusion which is the manufacturing process and PS stands for polystyrene which is the material.

Just for clarity to those reading.

[rbk]

Originally Posted by Buzzman

Actually this is not correct.

EPS = Expanded PolyStyrene Foam

XPS = EXtruded PolyStyrene Foam.

EPS is the stuff made from tiny balls of foam that is 'blown' under heat and pressure into a mould. Its the stuff large baulks of 'industrial grade' foam are made from.

XPS is the process by which Corecell and similar boat-building and modelling foams are made, extruded from a die in a 'continuous extrusion' method that produces a very fine air bubble and closed cell foam.

This is an important difference

Correct, always mix those two up, even more so when getting into type 1/2/8/9 etc

[Manateeman]

Original poster. The Richard Geer book on boat strength is great advice. Please read Principles of Yacht Design by Larsson. So to is the advice to go sailing on as many types and methods of construction as possible. Total vessel design is far more important than what material the hull is constructed from...don’t worry about myths...stick to science. For specific technical or engineering opinions, try boat design. net.
There is no perfect design, material nor method of construction.
After 50+ years of building vessels in almost every material, and with almost every building method...I chose a custom designed aluminum yacht.
At the very end, you can turn it back into beer barrels which is a requirement to keep a crew of manatees happy.
Happy trails to you
Captain Mark and his “Don’t write on me” manatees.

[Steely Dancer]

Originally Posted by Manateeman

After 50+ years of building vessels in almost every material, and with almost every building method...I chose a custom designed aluminum yacht.
At the very end, you can turn it back into beer barrels which is a requirement to keep a crew of manatees happy.
Happy trails to you
Captain Mark and his “Don’t write on me” manatees.

Hi, I found this thread after trying to get some info on how people feel about aluminum vs fiberglass sailboat hulls. I'm REALLY interested in this boat, but after seeing the ease with which Fiberglass can be patched, I worry a little that aluminum is much more intensive/expensive to repair, maintain, repaint, etc.

What are your thoughts?

[zstine]

Aluminum is easy to patch! You just weld it up. Don't be afraid to buy the AL boat, just add a boat buck for a welder and learn. not too hard.



Aluminum is a better material to build out of, but it takes a different skill set and more specialized tools to work. So there's more initial investment for the builder... But if you are looking at used boats and everything was equal except one was FRP and one AL. AL hands down is the better boat, IMO.

[Orion Jim]

Originally Posted by Steely Dancer

Hi, I found this thread after trying to get some info on how people feel about aluminum vs fiberglass sailboat hulls. I'm REALLY interested in this boat, but after seeing the ease with which Fiberglass can be patched, I worry a little that aluminum is much more intensive/expensive to repair, maintain, repaint, etc.

What are your thoughts?

A proven ocean cruiser....I would buy the ex-RAN in a heartbeat. Of course an intensive survey is necessary.