Just a thought, as I've absolutely no experience here ... but don't underestimate the force of the water drving down on your boat. If the magnets are weak enough for you to intentionally dislodge them (i.e., open the hatches) I'd be concerned that a crashing wave could unintentionally dislodge them, and a) you'd lose your hatch over the side, and even if you had a "leash" for your hatches so you wouldn't lose them, b) your boat would flood very quickly.  I would feel a lot safer with a more positive means of attaching the hatches.

Hi Kathy

That is a great idea !!!  I am about to start a wood duck hybrid and have given thought to different hatch hold downs.  Your idea is perfect.

I have lots of experience with rare earth magnets. You just need to be careful to select the right pull force.  If the force is to much you will not get the hatch to open. 

E-bay is a good place to find all kinds of rare earth magnets.

Lou

I'm with Lou on this one.  Rare earth magnets I think would be strong enough... and you will have to careful not to make it too strong.

As for the waves crashing down... yes, water is extremely powerfull and if I was building a boat for those conditions,  I would likely go a more traditional strap route or both... but for my wife's wood duck, that will never see big water, I now have a plan, thanks.

finally, here is my favourite store for rare earth magnets... and other fun stuff :)  http://www.leevalley.com

I'm not convinced.  Of course, I don't know what type of paddling Kathy is contemplating, or even what type of boat she's building, but I do know that the sea (considered broadly; lakes can get really nasty is a surprisngly short time, too) can deal much harsher blows than one might expect.  I've also personally known vessels to founder and people to be lost because sea conditions unexpectedly exceeded the capability of some of the boat's components.  In my area (the Chesapeake), for instance, I've seen calm summer days transform into violent thunderstorms, driving winds and steep chop in far less time than I could reach sheltered waters.  Even if the intent is to paddle or sail in shetered waters, I think it wise to be prepared for conditions to become far worse than you intend.

I don't know if I would go the magnet route personally but here is a good place to get high quailty small strong magnets. Great company too, I've bought my fare share from them.

http://www.supermagnetman.net

hi

would corrosion be an issue

regards from trev

What is the reason why you want magnets?  To avoid a strap?  There are other ways.

Kim

For those of you that haven't used them before, these are not your mom's refrigerator magnets. They are available in strengths that would keep holding on to each other even after the wood breaks up.

Issues would be finding a balance between a hold strong enough to keep the hatch on but still possible to open, keeping from getting one's fingers smashed between the magnets (the really big ones can amputate hands, let alone fingers) and keeping the magnets from smashing themselves (they can be kind of brittle). This makes the selection of magnet sizes and the design  of the opening mechanism a bit too finicky for me, which is why I decided to go with internal bungees. Magnets also weigh more than bungees and wooden hold-downs.

Corrosion should be OK as long as the boat is stored dry with the hatches opened and the magnets cleaned after each use.

Finally, you'll never be able to trust your compass again.

Good luck,

Laszlo

There are several guys on Nick's forum who have successfully used magnets for hatch hold downs. You might inquire here http://www.kayakforum.com/cgi-bin/Building/index.cgi and find out the pros and cons.

George K

Laszlo has made some very good points. 

If you are going to use a compass the magnets are a bad choice.

Corrosion is not an problem if you epoxy the magnets in and use one or two layers of glass over the top of the magnets. This will seal them water tight plus reduce the pull force to pull the hatch off.  I have rare earth magnets on the under side of my motorcycle and they show no corrosion after two years. ( I do ride in the rain ).

You do have to do lots of homework to find the right balance of pull force but I like to play around with stuff like that. For me it's what makes the building process fun.

Magnets are very heavy !!!  But the rare earth magnets you need for a hatch are very small.  About 1/2 inch dia. X 1/8 inch thick.  Just a few ounces total.

I am new to kayaks and I have lots to learn. I have never seen the internal bungee system but if that is what laszlo recommends then I will take a good look at that before I do anything with the hatch.

Lou

Rod Tait at Orca Boats' "how tos"

http://www.orcaboats.ca/o_howto.htm

These are PDF files. Note the file titled, "Installing Magnetic Hatches".

--

Ogata, eric

Thanks for all your comments and suggestions.  I'm still trying to decide if I'm going to use magnets, the CLC hidden hatch hold downs with under-deck bungees (but that seems to take up storage space), or something else.  I did find two interesting links in case anyone else is considering their hatch options:

Another description of magnet installation:

http://www.roguepaddler.com/ultim12.htm

A unique, hold down, but looks tricky to make:

http://www.kayakforum.com/cgi-bin/Building/index.cgi/md/read/id/172323

 I also read that as long as the magments are at least 18" from your compass it should be OK.  If I end up going with the magnets I'll test it and let you know.  

Kathy

Kathy,

Thanks for the links (not only did you give us details about the Moby latch, but you also let us know that our old buddy Kurt Maurer has an acting career) and do keep us posted if you use the magnets. Since the bungees are flexible, I've always been able to squidge them around to make room for cargo, so they haven't had a big impact that way.

Lou,

Everything I knew about internal bungees before I actually built a set I learned from John Harris (via the Shop Tips) and Ross Leidy. Check out their pages for good info, as well as my WD12 hatch hold-down page for  a quick but serviceable (cheap & unpolished) implementation.

Have fun all,

Laszlo

I initially used magnets on my boat and was really happy with them for a while.  However, I didn't seal them very well and once a little bit of water came into contact with them, they rusted amazingly fast.  When rare earth magnets rust, they expand to 3 times their normal size, which made it impossible to seal my hatches.  My advice would be to make triple sure they are well sealed in epoxy if you use them.  

OK, here's one more link on magnetic hatches, from Joe Greenley at Redfish Kayak.  He says they work well if installed correctly.  Very detailed description/photos of how he did the magnetic hatches on a cool custom kayak (it's worth looking just to see the kayak).  Plus an interesting twist to installing carry toggles without a big end pour farther down on the page.  

http://www.redfishkayak.com/livingston.htm

 Kathy

Just a follow up - I decided to go with the Moby hatch hold downs instead of magnets because I realized that the hatch sills that came with the CLC kit were not wide enough to accomodate the recommended size of rare earth magnets.  If anyone wants to see photos and a description of the Moby latches, it's located here (page 5 of the post):

http://www.westcoastpaddler.com/community/viewtopic.php?f=7&t=3517&start=100

I also did a little test on the pounds of pulling force required to open the hatches with the bungees that I used (I may eventually upgrade to thicker bungees, I'll see how it goes).  This is also described on the above site. 

Kathy

Kathy,

 Your Shearwater came out beautifully!  I love the attention to detail you put into every step!  Its those little things that take up so much time but make the boat uniquely yours.  (I went a little crazy on my compass block- a laminate of teak/cherry/ash/walnut-  and cherry/bronze toggles, but that was the extent of my creativity with this build).  I wish I had taken the time this winter to research strapless hatch hold-downs, as the Mobys look pretty darn good!  Ah, there's always the next build... :)

~Chris  

I have used rare earth magnets on 4 boats now, and I have not had any problems.  I have 80 1/2" X 1/16" magnets in my current boats for 3 hatches, with a total weight of only 7.5 oz, 2 oz less than the infernal bungees I used to use that took up too much space, were difficult to unhook and re-hook, and hooks that came free in hot weather.  I bury the magnets under a layer of fiberglass and put 3 fill coats on to insure no water ever gets to them.  On the retainer lip side they are sandwiched between carbon fiber and glass.  I have never had them let go during rolling or extremely rough water.  I have however had internal bungees let go from stress and age.  I put the magnets about 3" on centre from each other, each magnet has a 3.1 pound pull strength, gving the total pull strength for a 16 magnet arrangement 99.2 pounds.  This is adequate to keep the hatch very tight, but with a grab loop of 3/4" webbing to slip a finger in along one edge it can be pulled up with reasonable force.  I always put a tether on the hatch for safety's sake, but have never had to rely on it.

Bryan

my main concern would be fatigue of the supporting structure that holds the magnets in place and, as has already been mentioned, the effect on the compass. Although, I guess for that, carefully placed symmetrically around the perimeter, there would not be any net effect on the compass? And what about the out-of-plane effect. ie: the magnets are lower or higher than the compass plane and pulling the needle down(or up) and dragging on something within the compass. Just some thoughts. Seems like a neat idea. How much would it cost to rig a hatch like this?

I have built kayaks using several different hatch hold down methods including straps, internal bungee, Moby latches, bolt down and rare earth magnets.

Which to use, is obviously a personal decision but this may help.  First you must decide if you want a system designed to come open under pressure or one that will not come open under pressure.  The strap and bolt down methods are designed not to come open under pressure.  These methods offer the most secure way to hold down your hatch lids.

Internal bungee, Moby latches and magnets are designed to come open under pressure.  The idea being to get the optimum pressure that offers a tight seal but will allow the lid to be opened.

Ok, duh, I know this all sounds obvious but I am amazed at how many builders I’ve talked to that have not really thought these things through.

Two other factors should also be considered when deciding which method to use; namely aesthetics and ease of use.  The internal hold down systems using bungees, magnets and Moby latches leave a nice clean look that is aesthetically pleasing.  Having a smooth deck is nice to have when doing a re-entry. Having a buckle or a knob to get over when you are doing a cowboy can be painfulJ.    Removing your hatch lid while on the water (usually done by a paddle partner) is easier with some then others.  Both the Moby’s and internal bungee’s require a fair amount of dexterity to open and close; colder weather makes the effort even more challenging.  This can be especially challenging if the person helping you is not familiar with your set up.

After building and using the various methods, I have settled on the use of rare earth magnets.  Magnets are secure enough for my needs, I like the aesthetics of a clean deck and, if built properly, they are easy to open and close even on the water.  Your mileage may vary.

The problem of using a compass near magnets has been brought up and it merits consideration.  I have tested my kayaks from the cockpits using various types of compasses without any problems.  Keep in mind that magnets in your hatches can affect your paddling partners compass if they are along side your boat.

If you are worried about the magnets rusting (and they will if not properly protected), use an epoxy coated magnet for extra rust protection.  I have not had any problems so far using uncoated magnets but again YMMV.

I use Joe Greenly’s method to build my hatches.  However, I prefer to use ½ inch magnets (Joe uses ¾ inch) because they allow for a narrower lip which leaves a little larger opening to stuff things through.

Here are two good sources for purchase of magnets:

http://www.kjmagnetics.com/

http://www.magnet4less.com/

I use N52 magnets.

This post got longer then I intended, hope it is useful to you;

Good luck;

Dennis