I think that is a real problem with spring clamps. They can vary quite a bit in the amount of pressure they apply. The pressure can't be usefully adjusted. And they have pretty narrow range of opening which limits the places where they can be applied. They are cheap though and can be fast to place if you have something exactly the right width.

I became pretty enthusiastic about these Irwin quick-grip clamps that are carried at Home Despot during my last project. They set very easily,  and can be adjusted almost with one hand. Have a wide range of operation. And clamping pressure can be very finely adjusted with a kind of ratcheting squeeze grip. They also have permanently attached, firm plastic pads on the clamping surfaces to which epoxy does not stick. The pads prevent surface marring so you don't need to fiddle around with ancillary wooden scap "pads" that you would need using C clamps to prevent from leaving little round marks on the wood. Very easy to work with compared to spring clamps or C clamps. 

Probably sounds like a commercial I guess, but I have no affiliation with Irwin, or Home Despot for that matter. Just like those clamps. Can't get enough of them.

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Ogata (eric)

I've used spring clamps almost exclusively and have yet to have a boat come apart. C-clamps are more useful to me in traditional carpentry, as opposed to stitch & glue. With a gap-filling glue like epoxy, all you really need for strength is just enough pressure to distribute the glue over the whole joint and to keep the work from moving. Traditional carpenters' glues are what need the heavy pressure.

Never tried the Irwin clamps.

Laszlo

Irwin clamps are nice.  I have 4 and they are heavily used.  But pricey.  You won't run out and get 25 of them. 

I did get 25 two inch C clamps and would do it again if they ran off.

Also a dozen or so spring clamps are clipped on to me table for quick use.

If any of them run off I would replace them with the same. 

I'm with Laszlo on this one.  I used 3 c clamps during my build and the rest were spring clamps and pvc pipe clamps (from the shop tips). 

I didn't use any of the single-hand type clamps, though they are helpful sometimes.  I was building my boat on a fairly tight budget so I went for the cheapest tools I could get at the time.  I've been paddling my boat for 4 years now with no problems.

FrankP

It would be nice to just go to the store and buy lots and lots of clamps. In the real world I had to do with the raggle taggle collection I had. I prefer the c clamps because of the versatility. You can use them with almost no pressure or you can really crank it up. I have a few spring clamps and used them to quickly tack things in position while I leasurly positioned my mostly 3 and 4 inch c clamps.

I made a whole lot of pvc pipe clamps. I nested one in the other to double the pressure and that worked really well.

Since most of the boat gluing I did was with epoxy, it was important to get some squeeze out but not extreme and the control the c clamps give was good for that. Canadian Tire had a special for c clamps and I snatched a dozen or so. Nice addition to the clamp bucket.

In the end I had over75 clamps if you count the doubled up pipe clamps and this was sufficient.

Working alone the c clamp have an advantage in putting the gunwales on. I would bring the wood right up to the boat and slip a c clamp which I only clamped to the boat a little lower than the gunwale. That way the wood was held in position loosely at one end of the boat while I worked on clamping and final position at the other end. 

Christine

A WOMAN WITH 75 CLAMPS!!!  MY HEART IS A THUMPING!!! 

:O)

I had a dozen c-clamps left from an earlier project and used them on touchy areas like the hatch rims.  I prefer the spring clamps, though, because they are easy to use with one hand while the other hand holds the parts in place.  On the cockpit coaming, for instance, I clamped everything in place with six spring clamps, then added c-clamps in between them.  I have one Irvin clamp that was handy for occasional use, but too expensive to have a bunch on hand.  The spring clamps were 99cents each at Home Depot, so I didn't care if they got slobbered with epoxy.  I also used a couple of pipe clamps to align the hull and deck assemblies on my Shearwater.