I'm pretty new to this. I bought a 70's hobie 16 and it performs well! Though was only 450.00 w/trailer so it has a soft spot and rudders don't lock down. So I buy another boat after a couple weeks (83) has 3 sails... (1700.00) much better boat. Locking the rudders down "CLICKS" and I love that the rudder works so much better.

anyway - There is no junk on the hulls (no algea etc) they're clean and smooth. (no drag?) But for some reason, the 2nd (newer 83 boat) feels totally different from the older mid 70's boat. Here's how.

The better newer boat is SLOWER! As in it seems to drag as if Im' pulling something. (like a water anchor?)

This boat also LEANS! in the wind, much more easily... as in when the wind starts to pickup and its easy to lift one hull - it's also pretty balanced when lifting a hull. But seems SO SLOW have that much wind in the sail.

THE OLDER FIRST BOAT - doesn't seem to tip in same lower wind range, instead if goes FASTER! When it really is screaming - it will lift a hull and (tips more quickly, and doesn't seem to want to balance with one hull up.

ALL I CAN FIGURE is it's the sail. The older boat seems to have less bend in the sail. (battens more loose?) The newer boat that drags appears to have a LOT MORE BOW (CURVE) to the sail when I look up at it. I have the downhaul about the same, best I cam measure - and I have the boom torqued about the same. (I'm sailing the same) SO any idea why this might be? Is it the sail?

I like the better balance of the slower boat when lifting a hull, but it seems SO much slower. I can't figure it out. ( I suppose I could swap sails for a test).
?

Read elsewhere? maybe mast rake? is there a way to measure? I think I have the two boats setup pretty similar. There is a major difference in feel.

The more you rake your mast back, the more you have to rake your rudders under the boat. Drag is a problem I have right now with my set up in high winds. My rudders aren't raked under my boat enough and when the wind picks up it is like putting on the breaks. There is a way to measure both, but I can't remember where I saw them last. I've bought some new rudders (EPO's) and have found adjustable upper rudder castings so hopefully I will soon take care of this problem.

But someone with more experience than me may think that it is something totally different.

Set both boats up the same. Mast rake, rudder rake and toe in, etc. Use one set of sails on both boats so you've got a base line to work from.

Thats what it feels like - as if in the car pressing on the gas and break pedals at the same time. Then the wind is picking up so the boat leans a lot without going forward very fast.

The 2nd boat has (I belive) what you referred to as adjustable upper rudder castings? I THINK - as there is a slot and a screw of sorts on the top of the casting that isn't on my other boat. IS that what this adjustment is for? Rudder rake? IF they are raked ot far forward does that cause the drag? So if the rudders are over raked, I can rake the mast back more to help? Or unrake the rudders somme?

Yes. The adjustable upper castings have the screw and it is so you can adjust rudder rake without having to re-drill your rudders. As far as answering your other questions about proper rake, I'll have to leave them to someone with more technical knowledge that I have. For instance, many racers carry a certain measurement of mast rake and there is a way to get that measurement.
But then again, it may not be your rudders or your mast rake. Sailing too close to the wind (or pinching) will slow you down, and create a lot of lift. Over-sheeting can also cause you to slow down on certain points of sail.
If possible, I would try to find someone local that has been sailing a 16 for a while and let them give your boat a good look over. Maybe even sail with them and see how they set up their boat.
In addition, this is a wonderful site for catamaran sailors, but if you also post your questions on the hobie 16 forums you will likely get many more responses.

http://www.hobiecat.com/community/index.php?c=N

It sounds stupid, but make sure the rudders are installed on the proper sides.

The tiller arms angle in toward the center of the boat.

If that's not the problem, maybe the rudders aren't aligned properly. The trailing edge of the rudders should be about 1/8" further apart than the leading edges.

Maybe your older boat actually has newer (or less used) sails. Try sailing the new boat with your older boat's sails.

Rake - I thought I read that if raked properly the blocks will be nearly touching when hauled in tightly. (they are).

GIving it some thought... laying in bed - I THINK it may be the battens are tensioned to tight. There is a shape in the sale and often when I gybe - I look up at the sail is curved the opposite way, I have to shake the boom to pop the curve backward. How tight should the battens be?

And logically thinking - a sail that has a "U" shape would do as I stated above.... would tip the boat more, without releasing the wind on the back side thus making it not move forward. So I think that might be it. I SWAPPED to another sail and did get more forward movement - much better performance, but still not as fast as my older boat.

I then later found that one hull had a LOT of water in it.
Which brings up another question. What is common place for water to get in? The hulls are in excellent shape, not holes or chips or cracks that I can see. I have capsized it 3 times. (does that let water in?) and I think due to water in hull - we were unable to right the boat without our wave runner to pull it back up. But hull we stand on is pretty much submerged where we're on it. (so nothing to use as leverage.

Hull / Deck join
Pylons where they go through the deck
All fittings screwed in the transom (gudgeons, drain plug housing)

Lightly pressurize the hull using a shop vac set to blow. I've done this in the past by using the crevice tool and just hanging the tip of it in the drain plug opening while the hose is loosely taped below the rudder. Allow excess air to blow out of the hull past the vaccuum hose. DO NOT DIRECTLY CONNECT THE VACCUUM TO THE DRAIN PLUG! DO NOT USE AN AIR COMPRESSOR! It's suprisingly easy to explode a hull. I've seen the aftermath - which is non-repairaple.

Once you've got your pressure system going, use soapy water on all the suspect areas. If it leaks, you'll see bubbles or you'll hear and/or smell the leak.