as long as you use a long enough pole [3.2m] the spinny gives the bows loads of lift and the 16 can be driven hard under spinnaker and feels great.
The sad thing is that there are days when the stock 16 goes as fast [light winds]!
Turning block is 1350mm above hounds

Sorry, I dont have any pics and now sail F16. My advice is just do it. I have used FX1, F16 F18 and H16 spinnies and found the best was the 21mt F18 kite with 8.5 mt luff. The best pole length was 3.5mts. It is easy to sail single handed and takes out the tendancy for the boat to pitchpole so you can push hard downwind, flying one hull all the way. I used a snuffer as well which makes life easy. The best thing you can do to a H16.

Makes my enthousiastic anyway !!
However I got rather little spi experience (none on a H16) so I got some additional questions:

Mast rotation
Other cat sailors (Hobie & Nacra F18, Tornado a.o.) told me reduce mast rotation heavily and sheet in main sheet otherwise the mast won't survive. H16 has no controlled mast rotation - on the contrary. Sheeting in max will cause mast rotation to be max. Thus the mast will be in a rather weak position and most likely flex into S-shape....
I can think of ways to limit mast rotation but that will make my H16 not class legal anymore.

2 piece mast
My mast has a section and can be split for easy transportation. I can imagine this will make my mast even more vulnearable / fragile. Suitable for spi or special precautions required?

spi sail area
In addition to above: standard H16 spi seems to be approx 14 m2. The recommended F18 spi ± 21 m2. Former (why did they change to antoher cat ??) H16 sailors strongly recommended me to stick to 14 m2 max. Which is opposite your advice. Or should I (sailing alone..) limit myself to f.i. 3-4 Bft???

[Still eager to start spi sailing on my Hobie 16 !!]

H16 mast is built like a telgraph pole, even with a join! Just keep the traveller near center and the mainsail leech pretty straight [as the picture above] and mast behaves fine.

TeamVMG is quite right. The mast on a 16 is very strong but ALWAYS keep plenty of mainsheet tension to act as a rear stay. Do you have any spinnakers available? I would just use whatever you can get your hands on. I found the 21mt kite as easy as any to use. It seemed to have the power to keep the boat steady whereas the smaller ones let the boat stop and start in the waves. Dont worry too much about it. Just get whatever is available and start having fun. Then decide later which one might suit best.

Still been unable to obtain a used spi. In the meantime I saw a H16 which had - outside - re-inforcements on the nose tips. Another H16 user told me his cat was factory ready for use with spi and had re-inforced hulltips (inside). I own my H16 since 1992 and use it frequently and rather hard. Most likely my hulls are not prepaired. Should I do so and when yes what is proper procedure ?? The outside parts seems easiest way hope I can find them somewhere...

That would be a Hobie Cat Europe deal. We do not do H16s with spinnakers standard in the US. Contact them for specifics. www.hobie-cat.com

we had a 16 that was about that age when I first saw the bow tangs starting to fail
I turned the boat upside down and filled the channel under the hull join/lip with glass/resin tapering out about 300mm back on each side. Ooops, some carbon may have fallen in there too.
If you do this, put a greased bolt or something throught the bow tang hole first so that the fibres go either either side of it. Then, when you put a longer bolt in the bow tangs, you don't drill through all the reinforcing that you just did.

I can't believe that you can't find a second hand spinny in the netherlands! we have got a decent one and a trashed one here if you like. make me an offer

Took some years but finally decided to mount European standard spi because of 2 reasons:
- fellow H16 sailor joined me so we modified 2 cats simultaneously so we can continue catsailing together - with equal gear !
- sailing alone mostly the 17 m2 might be easier to handle than suggested alternative (f18 spi = 21 m2)

Results: 4-5 Bft and 2 man crew just fun. Did enjoy H16 sailing but this is adding another dimension. However alone and unsteady (but light !) wind will require some more training.
Hope to be able to upload pictures sometime

Enclosed pics of both cats. Orange for my german friend - mine is white !
Also shown the reinforcement of the bow which seems really necessary for "older" Hobie 16 cats.
Only for information - picture does not show one of our cats.
Intend to make a footstrap at the end of the hull and add a line with hook to secure myself against flying forward when the hulls submerge. Which does not always end up in a pitch pole we/I found out...
And trying to find a way to clear the mess of lines on the trampoline...