I am no accountant , but....suppose your boat's worth 80,000 (with a real survey). You take an $80,000 deduction from your INCOME not your TAXES. Now if your in , say , the 30% bracket that saves you $24000 in real dollars.
Now lets do the math. You gave away an $80,000 boat for $24,000 AND raised a flag with the IRS.
Why not sell it for $40,000 or even $30,000 (which is a steal) and you still come out ahead and no audit by the tax cops. Not particularly rocket science
Unless of course the boat in question is a genuine POS , worth $15,000(maybe)