Thanks for your response
For you to be treated as tax free in the UK, you have to achieve the status of not resident in the UK if you do not qualify for the Seafarers Earnings deduction, and whilst I can see you will qualify for 2015/2016 tax year - you will not for 2016/2017 - due to the way the occasions are mesured each time you leave, and each time you arraive to/from the UK
So I first will advise how the normal non residency rules work -
To be non resident (In HMRCs eyes) you must leave the UK to work AND live for at least a full tax year - during which time your visits back to the UK must not exceed more than 91 days. You at present with this arrangement will always excced the 91 dyas permitted as a return to the UK, and this along with the fact you are not actually leaving the UK to work and luve abroad, but are merely working out of the UK - so although you may be able to minupulate your time in the UK (for the second and future tax years( so that you do qualify for Seafarers Earnings deduction I have added a link here for the criteria for your information
This way you can see for yourself.
But if you do not qualify for this relief then you must consider that you will not actually be moving away from the UK you are merely going to be working out of it, and will return home every 16 weeks and home for 8 -
So for the tax year 2015/2016 which starts on 6th April you will have 16 weeks out and 8 in, then another 16 weeks out and 8 in , then the final 4 out.
So will be in for 16 weeks x 7 = 112 days- thats 21 days in excess of the permitted 91 days
So you either need to make sure that some of the two 8 weeks leave period you stay OUT of the UK and also monitor this for the future tax years too or keep on top of the eligibility for the Seafarers deduction.
Either way however, you must alert HMRC of this work abroad - on form P85 - link below for this form, Fill it in, send it to HMRC with your P45 (if you have just ceased employment) and they will arrange to set you up within self assessment as you will need to declare this income, and also complete a residency page and or seafarers deduction claim - both of which will require details your days in and out of the UK.
So make sure you keep all receipts and flight tickets etc as evidence of your time out of the UK
Link here for form P85
Let me know if I can be of any further assistance.