Mysefl I dont like diamond tarps.. ok in the summer but in the winter give very little protection to things on the ground, they can not be lowered to the ground to stop the airflow under them, if the rain is falling at an angle /getting blown, then anything on the ground will get wet...this leads me to say square or rectangle,
Size wise I have 3x3, 4x4, 4.5 x 3, and 4ish x 2ish (ponco Tarp)..
The 3x3 in my opinon is short for hammocking in the winter/rain unless you use it as a diamond.. but for me the reasons above count it out,
I find the 4.5 x 3 a bit too long you have to pick your trees well.. also if you take the tarp to ground the 3 meter lives you a low ridge, myself I find this a pain as I have to stoop under it...this I also find with the 3x3,
I have used the 4 x 4 quite a lot find it has plenty of room you can comfortably borito the ends in to form doors and have loads of room, the ridge is also at a nice hight for me and does not restict movement under the Tarp.. the amouint of room also give you loads of admin space it weather is a bit fowl, if you have not got a communial shelter....The only thnig I would say is the 4x4 can be a bit of a sail in V high winds... and can billow in.. I have not found this yet, but some have.
The smaller poncho type for me is just for warm sunny times...oh and of course boonie weekends..lol
I like the DD's, and have had no problems with them..they have external ridge line loops..and the tarp hangs under them, with a ridge line that runs under the tarp, but that could lead to rain running down the ridge line, under the tarp and driping inside the tarp on to what evers under it... if your hammocking , in to your sleeping kit...., yes you have hanging posibilitys of things , but just add an extra internal ridge line,
So to me the 4 x4 is teh best size for my needs...hope my thougths help
If you are getting a hammock as well do buy the carabiners and whoopies lings from the start
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