We are cruising full time on a Manta. Everything we own is on the boat and we are grossly overloaded - way past design specs. We seem to do 50-60% of wind
speed up to 8-9kts, then we reef to keep it around 8kt. For light air, we have a Doyle UPS that keeps us moving.
The Lagoon will have more elbow
space and load carrying ability, and possibly a small advantage in ultimate top end speed. It will probably go upwind a bit faster due to a much larger headsail, but not point any higher than the Manta.
The Manta will go dead down wind
on its white sails
faster than any other similar sized boat not using a spinnaker
due to the camber spar jib
. We are faster DDW on our whites than we are on our UPS.
Both of them will be about equal on a reach.
Don't worry about speed. I offer this opinion: you will always be keeping whatever boat you get to 8kt, unless you are just daysailing in calmer water
. It is just calmer, quieter and more livable that way. You will just have to trust me on that!
I don't know if you have been on the Lagoon yet, but it is a much larger boat than the Manta. This may be important with 3 kids. The Manta is better built and will probably have more comfort stuff (they come standard that way).
BTW, the comment from Capt. Bill above regarding the thinner floor is incorrect. The movement he describes is due to a change in manufacturing, where they no longer glassed the cabin
furniture directly to the bridgedeck and instead just sat it on the cabin sole
. Very stupid build decision. This was only done on the last few boats produced, so if you are looking at a Manta older than mid-2008, you are OK.