Like John I don't usually sponsor events like this which are really about the "adventure" for the participants rather than the charitable cause, and certainly not when the participants are complete strangers. Such events can be good for the charity just through the PR, but whilst what they are doing sounds like a fun challenge (from the limited detail you shared in the hard to read attachments) nothing about it sounds "that" hard.
Sadly your "outburst" above won't help convince me to donate, quite the opposite. However the following suggestions might be useful for you or anyone else trying to raise money in the future:
(1) Tell us about the charity and why it matters. I do know what the Firefighters Charity
does because they helped one of my suppliers' sons after an accident attending a shout that very nearly killed him; and I've donated to them in the past. I'd guess not everyone understands what they do.* I can also understand why UK Firefighters might feel a special association with their colleagues in New York, but I think you need to be realistic that ten years on, in times of financial prudence, the UK public are not necessarily going to be overwhelmed with generosity to help out the richest country in the world.
(2) If you are fundraising as a team a single team just giving page will probably get more attention. Whilst the link you've put up only has £130 of donations another page linked from their twitter feed has nearly £5k worth. I don't know if there are others. Generally people are like sheep and like to do what others do. If I was going to donate and saw than only a tiny number of people had gone before me (in fact fewer than were on the team) then I'd be a bit suspicious that the challenge wouldn't be completed.
(3) If you want people in the "boating" world to get behind a boating challenge - tell them about the boats, the equipment, the people, the training, the planning etc. People are more likely to give money to people they "know". Firstly to people I actually know, then maybe to people I feel I know on-line, and then possibly to inspiring people who have told a good story.
(4) If there are commercial sponsors (the Manchester Fire Service Page
suggests that Humber and Suzuki are lending equipment) then you really want to mention their help on your promotional material - since good publicity will attract other commercial donations which is where the real money is. But also because if people see companies associated with the 'challenge' it adds credibility that this is maybe more than a jolly.
(5) If people decide not to donate, accept that this is their choice and politely move on. Barracking people to support a charity is never a good idea. Some people just don't do it, others can't afford it, and others already are giving lots either in time or in money to their own "pet projects". Whatever their reasons for not giving - it is not a tax and they should be free not to donate.
(6) If the team are paying for fuel, accomodation etc themselves then make it explicit. Otherwise people will assume this is a "cost of fundraising". Then make sure that the people you are asking really see this as a challenge. Stand out from the crowd. There are three people all raising cash on here at the moment with "long distance rib trips".
* I'll save for another day the debate about whether supporting the charity actually removes an obligation from Governments to support public servants injured in the line of duty.