I understand your idea for wanting for increase upper body strength, but increases in lower body strength will indirectly increase your upper body strength. So lower body strength cannot be neglected. That’s why strength is considered to be “general”. You don’t see sprinters just working out their legs do you?
Along with general strengthening, specific exercises relating to the sport can also be used. Cable shoulder work would be a good start.
1> Search this site for “swimming”,“swimmer”,“swim”. You’ll find a number of threads in the archive.
2> I have never seen successful swimmers adopting Westside templates in their strength training.
3> As from the post above,do not neglect lower body strength for swimmers. Only considering the quantity of upper body work swimmers are already performing in the water,you simply would find extremely difficult to impact UB strength level significantly with an overly specific program.
4> The more you’ll be able to consider the GENERAL nature of strength (as of the stimulus itself),the more options you’ll have available,and the more chances to be successful you’ll give to your job,with swimmers and different athletes.
Wherever you got that 15% from,be at least very careful if really taking that into consideration.
Look for Gennadi Touretski’s -Alexander Popov’s coach- analysis of limiting factors of the 50/100m events in the pool, look at what Frank Busch is doing with the South African sprinters Schoeman and Neetyhling lower body work wise.
Be assured of one single factor: the shorter the distance of the event your swimmers are preparing for,the more their performance will be limited by the quality of their lower body overall contribution.
Waterpolo might be completely a different story. I have been quite successful consulting a WP team adopting similar criteria I have used for soccer while taking into consideration the different muscle involvement characteristics of the sport.
I would still avoid a Westside (as any powerlifting) approach,although I know their methods have been implemented by some American Football teams with some success,possibly offering an additional option in this direction.
Other sources you might want to investigate further before assuming anything about strength training for swimming related events are USA Swimming site,and the ASCA World Clinic Books from the last few years,where a lot of empirical evidence and research have been presented by people who have devoted long years to the contribution to the sport.
And with some success.