Chesapeake 18 payload

Being 6'5 255 lbs (decent shape being a firefighter), I have a kayak camping trip planned this summer. I'm getting close to finishing my Chesapeake 18 hybrid build and started playing with some numbers. The trip is in a large bay along the coast so I'll have to bring my own water. By the time I'm done I'll probably be within 20-30 lbs of the maximum listed "payload". 

Has anyone pushed this payload limit? Was there any buffer zone set to this number or will water be up to my cockpit coaming? I surprised the HC Great Auk has almost twice the payload limit with pretty close dimensions. 


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RE: Chesapeake 18 payload

John at CLC could probably give you a more detailed treatment.....

but in general, if a boat is rated to X payload limit and Y paddler limit, there is plenty of buffer built in.

in orther words, you should not be concerned if you are right up at the top of the are not in anyway in danger of swamping or having the boat behave in 'strange' ways.  it's when you are outside of these limits that you need to start to pay attention.

if you are in the 'range' this is where the boat was designed to be and it should maintain the safety margins and handling characteristics that the designer intended (the boat is within its design lines).

the tricky question is how do you 'discuss' what happens when you are outside the range in a reasonable way.....that does not lead to a slippery slope path to bad things.  a couple pounds over....with typical margins on a boat like this....i doubt is going to make a a lot of difference....but as for me....i like to stay between the lines.

the designer, however, is in the best position to discuss what is likely to happen under different over-loading scenarios.


RE: Chesapeake 18 payload

"......will the water be up to the cockpit combing?"  .......................that's easy. Pack the boat for camping and go paddle it.    

Will it behave? .....load and go paddle a day trip.  With kit boats like this with the variables in construction quality and techbniques the limits have to be a little gray. The design limits assume the same construction. Who knows the quality of your construciton until you test it?  It might be better or ........Load it up and try it in some calm water then head for some waves...........or boat wakes and compare the bow bouyancy on a series of waves near shore and near home on a day trip.  Check out lateral stability loaded and unloades.  It should be different but not unmanageable.  Get used to it before the big trip.  

RE: Chesapeake 18 payload

Grumpy is a pragamatist....i appreciate his wisdom.

that said, there is a reason that boats have specs....and the chesapeak design leaves plenty of margin and you won't be anything close to the coaming if you stay within the design loadings.

just to be clear....the max payload is not anywhere close to the 'sinking' weight....which would be substantially higher.  a back of the envelope bouyancy (or the weight required to sink it) calculation of  diamond-shaped kayak with nine inch sides and 18 feet long and 24 inches at its max beam (a 'simplified chesapeake 18) is 62lbs * 1/2(2*18)*3/4 or 837 lbs.   so at 350lbs max recommended payload (plus 70 lbs for the boat itself. or 420lbs)...the boat (assuming the 9 inch sides) is only going to be about 4.5 inches in the water leaving you with another 4.5 inches of side above the water line.

another interesting rough calculation is how much weight it takes to sink the boat an additional inch from its design waterline at max load. which is 62lbs* 1/12*1/2(2*18)  or about 92 lbs per inch.

it would be a real drag if you had to 'test' the basics of design displacement ranges...and i don't think you really need to.

now grumpy does have some other points....but i would look at them with a slightly different perspective.  you probably don't want a 'serious' voyage to be your first experience with a boat period and certainly not a large boat at its maxed out weight.  

physically handling a heavy boat, if you are used to handling empty kayaks, is going to be an adjustment.   remember a payload of ~ 100 lbs leaves you with 170lbs of boat...which is not a trivial amount of weight to handle or manage in certain conditions.  for example, i would want to think about the landings and put i dealing with rocks and concrete....or do i expect nice sandy beaches.   you can really tear up the bottom of a 170 lbs empty weight boat on the wrong surface.  a bad surf landing in a 170 lbs kayak can break your neck.   but i am not sure the cautions are significantly beyond paddling the same boat with no additional cargo. (remember....fully's only sinking a little over another inch vs unloaded)

as for 'can the boat structurally handle it'.....the general boat building techniques of a CLC are very robust.....and unless you were doing some awful poor construction....not a place i would worry about beyond normal see trials and the general notion that i would not want my payload to be a barbell or some other highly concentrated weight that could overstress a panel.

anyway....just my 2 cents.....but i thought a couple figures would help you put things in context.




RE: Chesapeake 18 payload

just a quick adder to my last address the the question of why the HC great auc had such a high payload.

two things to keep in mind.....displacement is related to enclosed volume.....and the math of it is a relatively small increases in external dimensions can lead to fairly large displacement differences.  (e.g., a two inch cube filled with water weighs 4X more than a one inch cube).

so how does the hc great auk do it?  first, its almost 6 inches widers (30 inches vs 24) than a chesapeake 18.  and two....its a lot less pointy....and carries that maximum width quite far out to the bow and stern  (so it is not like a diamond...but more like an elongated oval)......the design draft is also about 5 inches (leaving about 2.5 inches clear of the water line).   so this works out to about 630 lbs using the figures on the guilemots site.

that said, with that shape, sinking it one additional inch from its design waterline at max recommended weight requires an additional137 lbs.  eyeballing the would probably need an additonal 400 lbs to on top of its max recommended weight to actually sink it. 

all the best, 


RE: Chesapeake 18 payload

Thanks, Grumpy's did have some down and dirty logic which was good humor. I would never attempt a trip where I run close to the payload capacity without first testing it, as I plan to. The only time I didn't do a test was using my existing plastic kayak that has a 475lb payload and I knew I was going to be well within the limits. 

My goal when posting the question was possibly having someone who has loaded the kayak to this limit and provide some feedback on how it affected boyancy and performance before I do test it. I appriciate all the formulas and calculated input though. Good information on how boyancy is derived on the kayak designs. 

The extra load does make for interesting launches and landings. I'll be changing my ways performing these as compared to my plastic kayak. I've taken some measure by applying a couple rub-strips.  


RE: Chesapeake 18 payload

   You may also want to try different arrangements of your heaviest items between the front and back storage spaces. This could raise or lower the bow or stern and can also affect handling of the kayak. It is best have a neutral balance as if the kayak is not loaded but there cold be times you might want to adjsut this.

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