Had a quick look on the web and it looks a smart boat. I have no experience of surface piercing props but this video on YouTube may help you find a starting point .
Seems quite fast and any faster will take you back to your flying days. 😀 LiPos will be required to get this sort of performance and I suggest you have some sort of rescue boat as the model will flip at some point.
We have members in my club who favour fast boats and I know they all change setups constantly to Improve the speed. There is lots of tork involved and propshafts can and do break.
Good luck and I look forward to seeing your model on the water

HI Dave,
I had a ducted fan driven sabre jet free flight model about1952, since then my aircraft had props. the boat I have just started is 1/10 scale sport hydro 1969 notre dame. you can find it on the internet. it will have a surface piercing prop with a flexable drive shaft, the only problem I have is knowing which motor to use to get a fast boat first time round.

To match your IC performance Brushless is definitely the best option. At 40" your model is not that big so weight is possibly a major consideration, so NiMh or LiPo should be the power of choice. if you are new to LiPo do follow the instructions and use a proper balanced charger.
Looking at hydroplanes on Google suggests they use jet propulsion, so are you considering some form of ducted fan?
We have members in my club who use ducted fans on skimmer type models and with some careful setting up they look very Impressive and really skoot along.
As model flyer you possibly have some knowledge of ducted fans and I have seen them advertised with suitable motors. I used to fly model planes but never had experience of ducted fans, but I guess you can get thrust details and marry this to your model. Giant Shark have a section on EDF units http://www.giantshark.co.uk/sector/94/edf so this may give you some help.
Do you have plans/pics of your model? You may get more help if members know exactly the sort of Hydroplane you are building. 😀

HI Dave, have been building quarter scale aircraft and large model boats for the last fifty years but have always use I/c engines. The latest model is a scale american hydroplane, the fullsize boat used a spitfire engine.
best wishes
navyman (ex-rn)

HI Navyman
The fastest motors are usually brushless with LiPo batteries, but this may be costly if you are new to R/C and have never used this technology before.
Please give a bit more info re your previous modelling experience so we can give the best advice to suit your expectations.