In reply to 5cifi:
This is a troll. Until I saw the it was the stuff of Scifi. I hope you consider that the advice you have been given has come from predominately climbers.
In the spirit of the advice you have been given, I can only endorse their opinions. It's easily doable.
Ignore the fact you have no knowledge of the sea. Or the sea going qualities of a baby speedboat, or knowledge of seamanship, or the sea, or tides and their effect on direct line travel, or how far you'll get on a tank of juice, or handling a little boat in rough seas (Actually not a problem because it'll sink). Do you know how far it is from Blackpool?
So please go and try it. I do love it when the news has headlines such as "Three men in a Speedboat drown trying to cross the Irish sea".
However I'll give you the following advice based on many years handling a variety of large and small craft, some of it professionally.
A 16' Speedboat can only be handled safely in easy seas, in small swells and little wind. A little above that and it takes extreme skill to handle. They are simply not designed to travel open seas. The wind on the crests of waves will flip one like a playing card. It doesn't matter what skill you have. "Turning round and going back" when you are 20 miles out to sea may not work. One reason being that if the weather is worsening, then you are faced with 20 miles of worsening weather. So when you start shitting yourselves 20 miles out because it's getting scary, you'll have another 20 miles after turning round to go back - in worse weather!!
You need another engine in any case at sea. a 2.5 hp has been suggested. Use this as a sea anchor. (OK you don't know what that is but never mind) A 2.5hp motor on the Irish Sea won't even stop you drifting in a tideway or against a fresh breeze!!!!!! And don't forget that a larger spare will upset the trim of the boat, lifting the bow higher (thats the pointy thing at the front). Go to quick and the wind will get under her and you'll do a backward flip in the thing.
Have you worked out how much extra fuel you need - don't forget a 20% safety margin -and how much it'll weigh? And the effect on the speedy boat's trim and safe loading capacity?
Have you any knowledge of taking into account tidal/wind drift when setting a compass bearing? You'll need to work out the tidal flow at different times to offset the angle you travel at or you'll end up describing a giant 'S' Across the Irish sea which will increase your fuel consumption too and may turn you across tidal races which;ll be fun.
Do remember that as a small manoeuvrable boat YOU will be expected to avoid ALL larger craft. And it's quite likely that some larger vessels won't have a look out and larger ones, such as tankers or container ships may not be able to see anything as small as a 16' speedy boat thing if your'e against the sun. How does your boaty thing handle in the swell created by an oil tanker?
You'll need to think out some contingency plans too. A mobile phone will not work out of sight of land. How will you call for help in the unlikely event that you need help? You'll buy a VHF handheld of course!!
Do you have an operators license for it? You'll need to know the right procedures too. Shouting "Help were sinking" on the wrong channel won't endear you to the pilots taking tankers into Liverpool and if anyone takes you seriously how will you tell them where you are and what help you need?
NB A large merchant vessel will not bother even try and pick you up in a little speedy boaty thingy. It's doesn't have the manoeuvrability.
I'll keep my eyes and ears open for the TV news anyway. Good luck.