Cruisers Forum

Join CruisersForum Today

Thread Tools Rate Thread Display Modes
Old 23-12-2010, 14:08   #1
Registered User
stevensuf's Avatar

Join Date: Dec 2010
Location: Back in Scotland!
Boat: Gib sea 43
Posts: 826
Images: 10
Making a Boat Unsinkable with Expanding Foam

I know etap and many cat manufacturers have done the like , but few yacht builders have done so, now I'm wondering if it would be possible to retrofit a yacht to make it unsinkable, say a 45 foot 11,000kg yacht with say a 3500kg lead keel.

I know 1 sqm = 1000kg buoyancy with air so a little less with expanding foam, but does anyone know offhand the average density of a modern production yacht?

I mean you only have to make the average density a little less than water for the whole lot not to sink right under, maybe float a foot or so when flooded.

Are modern aluminium masts hollow? Would it be possible to fill with foam or a bad idea? It certainly would make the boat self right quicker in a capsize situation (just like a wooden mast?)

I know you;d have to sacrifice storage space to do this, bit im sure there are so many voids you could fill it would not be too intrusive to do.

Any and all ideas welcome, thanks.

stevensuf is offline   Reply With Quote
Old 23-12-2010, 14:31   #2
Senior Cruiser

Cruisers Forum Supporter

Join Date: Dec 2006
Location: Seattle
Boat: Cal 40
Posts: 2,376
Images: 7
Yachtsaver was a company that made bags that inflated automatically like a liferaft inside your boat. Took up less room until needed. Don't know if someone else is doing it.

I've thought about making one or two watertight compartments. On my boat if I seal up the holes in the bulkhead to the vberth, put a rubber gasket on the sliding door, a collision causing a big hole on the bow could be contained.

The mast wanting to float compared to the keel trying the right the boat is tiny, and most times the mast isn't going to be there anymore anyway.


cal40john is offline   Reply With Quote
Old 23-12-2010, 14:37   #3
Registered User

Join Date: Jan 2010
Location: Wells, Vt
Boat: 42ft Colvin Gazelle - TLA HLA
Posts: 504
I have seen several boats that have made their forward storage areas under the v birth into "water tight" compartments. Same with heads and other areas that can be closed off by seeling and water tight doors. Sometimes bulkheads. Theoretically they are both air chabers and water containment areas in case of holing. Potentially great idea and if building it might very well be worth designing in. Retrofit might be harder. Foam? You loose a lot of storage and add more weight. Most masts run rigging inside. Not much volume iether.
ConradG is offline   Reply With Quote
Old 23-12-2010, 14:45   #4
Registered User
stevensuf's Avatar

Join Date: Dec 2010
Location: Back in Scotland!
Boat: Gib sea 43
Posts: 826
Images: 10
Thanks john,
The airbag idea is a simple solution i have thought of that one as well.
I have done a few quick calculations lead being 11 times denser than water
Ie that makes about 3 cubic meters of foam for the keel.

thus the keel is the main problem, fiberglass composite only being 1.6 times denser so less buoyancy required for the main hull, though i have no idea what percentage of the weight is made up from the hull (any ideas?).

I'm with you on the mast capsize thing, i do appreciate the few masts do survive such an event, but surely an aluminum mast filled with expanded foam would add to buoyancy and be much much stronger?
stevensuf is offline   Reply With Quote
Old 23-12-2010, 14:51   #5
Freelance Delivery Skipper..
boatman61's Avatar

Community Sponsor
Cruisers Forum Supporter

Join Date: Jan 2010
Location: Europe
Posts: 18,343
Images: 2
Send a message via Skype™ to boatman61

Originally Posted by stevensuf View Post
I'm with you on the mast capsize thing, i do appreciate the few masts do survive such an event, but surely an aluminum mast filled with expanded foam would add to buoyancy and be much much stronger?
I presume the idea being an aid to 'selfrighting' due to the increased bouyancy pushing up in oppsite to the keel downwards... speeding the roll to completion... or have I lost the plot.... again
I do not exist to impress the world.
I exist to live my life in a way that will make me happy.

boatman61 is offline   Reply With Quote
Old 23-12-2010, 15:03   #6
Moderator Emeritus
Pblais's Avatar

Join Date: Mar 2003
Location: Hayes, VA
Boat: Gozzard 36
Posts: 8,700
Images: 15
Send a message via Skype™ to Pblais
You could add buoyancy to a boat but I'm not sure I would.

The mast is hollow but in a big knockdown you'll lose it (they break off). You want bolt cutters to cut the shrouds and let it go. Boats don't sink straight down most of the time. Adding foam to the mast wouldn't make the righting motion change enough to really matter. If the mast goes over and under it means you got smacked pretty hard. It will right and you might have water below and not sink. You probably break a shoulder and bleed to death. You can't pick the precise scenario. You might come back up and be able to motor some place safe.

If you cruise you really can't sacrifice storage space because there is never enough. I guess I would want to know the context of why you feel this is a seriously important issue that you'll leave behind other items proven to save your life? Even if the boat didn't sink it could be smashed to bits. A direct lightning strike could kill you but not hurt the boat. Trying to redesign a boat isn't always the best approach.

If you never sank you wouldn't have room for all the extra safety gear you could have taken. Sinking may be a danger but there are 100 more scenarios that are more common in comparison that can be prevented with proper equipment and more importantly with the training and skill to use it. It's not unheard of for the people to leave in a raft and the boat to survive. A raft is the better solution to a sinking boat. The boat is almost under water and you inflate the raft and climb up into the raft. The boat could break up and "unsinkable" becomes moot.

Consider the option where your training and experience minimizes your risk of sinking. Cutting the odds is risk sound management. A smarter you is the best investment and the most confidence. In the spectrum of all things possible you can't pick and choose one at a time and beat the odds.

So the weather seems wrong and you have studied the weather by training and logging and maybe hedge and paid for a routing service. You stay put and don't leave the anchorage even though you want to be some place. The boat is 100% safe and can't sink because you "are not at the place where you would have been toast". You'll sleep better taking that approach rather than oh we don't have any storage and don't have gear but we won't sink! You can pick your battles and be ahead statistically! Ok you don't have a spare anchor or the extra chain or the extra fuel and water but you'll die on the surface or in the rocks or starve to death. You can't think in one dimension. The boat sinking may not be the worst thing you have to face given the almost infinite alternatives that could lead to your demise.
Paul Blais
s/v Bright Eyes Gozzard 36
37 15.7 N 76 28.9 W
Pblais is offline   Reply With Quote
Old 23-12-2010, 15:24   #7
Senior Cruiser
Vasco's Avatar

Cruisers Forum Supporter

Join Date: Apr 2004
Location: Toronto
Boat: CS36Merlin, "La Belle Aurore" Ben393 "Breathless"
Posts: 6,819
I looked into the air bags years ago, it took up all my storage room! Better to spend the money on a good life raft.
Rick I
Toronto in summer, Bahamas in winter.
Vasco is offline   Reply With Quote
Old 23-12-2010, 15:38   #8
Senior Cruiser
delmarrey's Avatar

Cruisers Forum Supporter

Join Date: Mar 2003
Location: Somewhere along the US West Coast
Boat: Modified Choate 40
Posts: 10,474
Images: 122
Originally Posted by Vasco View Post
I looked into the air bags years ago, it took up all my storage room! Better to spend the money on a good life raft.
My thoughts as well. In the USA and Canada, the two that I know of, only require floatation in boats smaller then, I think, 26'. Anything larger then that can carry life rafts, pumps and/or dewatering gear.
Faithful are the Wounds of a Friend, but the Kisses of the Enemy are Deceitful!
A nation of sheep breeds a government of wolves!

Take nothing but pictures, leave nothing but footprints!
delmarrey is offline   Reply With Quote
Old 23-12-2010, 16:37   #9
Registered User
bewitched's Avatar

Join Date: Sep 2009
Posts: 885
Images: 3
Originally Posted by cal40john View Post
I've thought about making one or two watertight compartments.
I've often wondered why more boat builders don't do this, especially in the bow areas. It's not all that difficult to achieve and with watertight hatches there is no loss of utility for storage.

I think the aim would be to contain the incoming water to specific areas of the boat, rather than trying to keep the boat afloat when it is completely full of water. (which would require a total volume or airtight compartments equivalent to the below water line internal volume of your boat - which is a lot)
bewitched is offline   Reply With Quote
Old 23-12-2010, 18:38   #10
Registered User

Join Date: Sep 2009
Location: Mackay,QLD, Australia
Boat: planning a approx 45ft cat
Posts: 3,393
Images: 3
One manufacturer of power cruisers in Australia(either Maratimo or Riveria) has put considerable bouyancy in stern alongside engine bays in oocase of flooding engine room from damage to IPS drives and vessel sinking from stern.

Re sailing vessel in iam looking towards an unsinkable foam sandwich catamaran.
downunder is online now   Reply With Quote
Old 23-12-2010, 19:03   #11
Registered User
Ike's Avatar

Join Date: Oct 2008
Location: USA
Boat: FL12 12 ft rowboat
Posts: 184
In the US, Canada and nations that use the ISO standards flotation is required in some boats (not all) under 20 feet (6m) Some manufacturers put flotation in their boats up to about 26 feet but this depends a lot on the type of boat. The reason for this is not added weight. It is simply a matter of the volume of flotation that would be required to support a larger boats. The interior volume of a boat increases geometrically not linearly. I increases very rapidly in boats larger than about 22 feet. what it amounts to is you add one foot of length to say a 30 foot boat, you have added 4 or five cubic feet of volume, and the added volume increases for each added foot of length added.

So a boat 30 feet would require a hell of a lot of foam to make it unsinkable, especially a sailboat with a keel. So at this point designers start looking at other more important factors such as stability. They design watertight bulkheads and compartments. Bilge pumps are added to handle some amounts of water (but a bucket and a scared man are still the best).

And Yes Etap does it but most of that flotation is foam sandwich in the hull, deck and cabins. I have looked at their boats and I know what they say, but I honestly don't think they have enough flotation to keep their larger sailboats afloat.

As has been said, prepare your self for the worst possible scenario. Spend your money on a good liferaft, a VHF, an Epirb, and maybe even survival suits. Learn how to use it all. Drill until you can do it in pitch dark in horrible weather. That's what we do in the USCG, drill drill drill until it can be done in your sleep. The first time I was in an emergency that wasn't a drill I didn't even realize it until I was at my station and ready. Then some one said to me, did they say this wasn't a drill?? That is how ready you need to be.

And the odds are, you'll never need this stuff, but when you do, you really need it! One last comment, most of the boats abandoned at sea survive just fine all by themselves. Usually its the people who can't take it. The USCG airlifts a lot of people who really could have survived on their own if they had just prepared themselves better.
"Dont tell me I can't, tell me how I can"
Ike is offline   Reply With Quote
Old 23-12-2010, 19:25   #12
Registered User
atoll's Avatar

Join Date: Mar 2010
Location: gettin naughty on the beach in cornwall
Boat: 63 custom alloy sloop,macwester26,signet20,prout snowgoose 37 elite catamaran!
Posts: 8,640
Images: 75
we have 5 watertight bulkheads,and a good supply of blow up dolls,in case of emergency................
latest project
atoll is offline   Reply With Quote
Old 23-12-2010, 19:33   #13
Registered User

Join Date: Dec 2008
Location: ontario canada
Boat: grampian 26
Posts: 1,743
If I was that worried about my boat sinking I wouldn't go to sea. It's not like the bottom of the ocean is waist deep in sunken sailboats.
perchance is offline   Reply With Quote
Old 23-12-2010, 20:18   #14
Registered User
timbenner's Avatar

Join Date: Jan 2007
Location: Ponte Vedra Beach, FL
Boat: Lagoon 380, 38', I Dream of Jeanne
Posts: 295
Images: 7
If you're worried about sinking, buy a catamaran, they rarely sink. Plus you have plenty of storage.
timbenner is offline   Reply With Quote
Old 23-12-2010, 20:28   #15
Senior Cruiser
44'cruisingcat's Avatar

Cruisers Forum Supporter

Join Date: Sep 2006
Posts: 6,188
Images: 69
Lee Roper, a friend of mine, designed his own boat to be unsinkable. He has basically filled a fair bit of what would normally be storage, with foam. It actually paid off for him too - he hit some rocks and holed his hull, but was able to stay afloat until he could effect a temporary repair and get to a marina.

While he has given up some storage space, he's still able to cruise and live full-time on the boat, which is a 43' mono.

44'cruisingcat is online now   Reply With Quote

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Similar Threads
Thread Thread Starter Forum Replies Last Post
Where to Get Foam to Make Boat Unsinkable boat_alexandra Construction, Maintenance & Refit 60 18-01-2014 05:44
Making Cash with Your Boat cathyoz Boat Ownership & Making a Living 0 26-06-2010 14:34
Making the Jump to a Boat Project flatlander Construction, Maintenance & Refit 5 08-09-2009 20:37
expanding the fuel tank jay75 Construction, Maintenance & Refit 7 12-11-2008 16:04

Our Communities

Our communities encompass many different hobbies and interests, but each one is built on friendly, intelligent membership.

» More about our Communities

Automotive Communities

Our Automotive communities encompass many different makes and models. From U.S. domestics to European Saloons.

» More about our Automotive Communities

Marine Communities

Our Marine websites focus on Cruising and Sailing Vessels, including forums and the largest cruising Wiki project on the web today.

» More about our Marine Communities

Copyright 2002-2015 Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 21:59.

Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2016, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2016, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.