Hey there, new to the forums. I'd never heard of HIIT before I joined the forums but it sounds interesting. Whats the major difference between HIIT and Fartlek?

I'm an 18yr old lightweight rower seeking selection for the state U23 LW 4- in december next year.
Atm I do 2 on water sessions of 120-180mins, but that will increase to four sessions a week in the next three weeks, i also do one session of weights in the gym with a lightweight rowing specific PT as well as two sessions on the bike for around 45mins (mix up hills, standard intervals, steady state cardio) at around 80-85% HR. I also walk to and from uni (5km each way), work (4km each way) and run to rowing training in the morning (3km each way). MHR is 209, RHR is anywhere from 45-58 (so about 52 average) depending on the morning. I'd be interested in giving HITT a try. Thinking about it I would probably look to do it on a stationary bike (i'm not a huge fan of running, even though i run to rowing, as i have problems with my knee joints and have also suffered from shin splints in the past). My program changes in 4 weeks so then it will look like

Day 1: Rowing (4.45am 7.30isham),
Day 2: Weights (10am) then 45mins cycling at 80-85%HR (hills or intervals)
Day 3: Rowing (4.45am - 7.30isham), 45mins cycling at 80-85%HR (hills or intervals) (1pm)
Day 4: Core Stability (5.30pm)
Day 5: Rowing (4.45am - 7.30isham),
Day 6: Rowing (4.45am - 7.30isham), 5mins cycling at 80-85%HR (hills or intervals) (1pm)
Day 7: Cricket (all day, every fortnight)

so total of 9 sessions (not counting cricket which is pretty cruisy)
With a program like that would it be beneficial to drop the current cycling program and go with HIIT in place of it? If so what sort of W:R should i be looking at? And will it be of benefit to me for rowing? Out of interest could HIIT type work be done in the boat (different to conventional intervals)?

Thanks in advance