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Port Dinorwic / Y Felinheli (almanac stub) and Menai Strait

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Courtesy Flag

Flag, Red Ensign


From South 53° 06.450N 004°25.001 (Caernarfon Bar Light) From North 53°18.82N 004° 02.28W


AC 1464-1 Menai Strait South; AC 1464-2 Menai Strait North; AC 1464-3 The Swellies; AC 1970 Caernarfon Bay; SC5609 North West Wales including the Menai Strait; Imray C52 Cardigan Bay to Liverpool (includes plan of Menai Strait)

Rules & Regulations

There is a 5kt speed limit in parts of the Strait marked by “5 Knot” buoys


The Swellies. Strong currents and whirlies everywhere at the strong parts of the tide

Tidal Data Times & Range

HW Port Dinorwic is 20 mins before HW Holyhead MHWS 5.6m MHWN 4.4m MLWN 2.0m MLWS 0.8m   (links)

This site is designed for slower, roaming broadband connections, like you would get at sea, so it needs JavaScript enabled to expand the text.

General Description

Harbour Master tel 01248 671500; VHF #80;
Port Dinorwic Sailing Club tel 01248 671147,

Port Dinorwic (run by the Marina Group) is situated 2 miles from the Britannia Bridge on the Caernarfon side and consists of two separate entities; they have berths in the locked, tree lined creek off the Menai Strait and a small drying harbour just to the south of that which has pontoons. There are moorings outside that in the Strait which are maintained by the Caernarfon CC but let by the Marina.  The pontooned harbour has the obvious advantage of easy access to the Strait but the disadvantage in that all the marina services are in the creek.  The Sailing Club is half a mile away along Beach Road.

The area around the marina and harbour is mainly residential though there are a few restaurants/cafes outside the marina gate and some shops along the top road towards the harbour. There is also a hotel across the bridge on the side opposite the Marina Office.

Beyond the Sailing Club towards Caernarfon there are a couple of boatyards/ marine services business which you can find in the local business directory at the foot of this article.


The Strait itself is an obvious shortcut from West Wales to Liverpool (you save about fifteen miles) and vice versa but you will have to juggle the strong tidal streams to make it in a oner so this location would be a pleasant stopping off point


This is where the fun starts. There are very strong...............

....... tidal streams in the Strait and they do not conform to any particular logic.  We at VMH have not navigated this Strait but we have trawled all sources of information, given links to a couple of useful videos and there are more to be found on YouTube

The main Flood tide enters at Caernarfon much earlier (sometimes as much as 6 hours) than at the northern end by Puffin Island. As the flood gains strength from Puffin Island the sjoin moves slowly through the Strait southbound giving a body of slack water moving down the Strait until eventually the whole Strait is flowing South. Then the Caernarfon flood begins again, chasing the weakening Puffin Island flood back north until the whole strait becomes a northward ebb (or flood?)  To confuse you even more we have included a diagram of the tidal streams within the Strait in our Navigational Gallery. You really want to arrive at the Swellies at HW slack (about 2hours before HW Liverpool); it is perfectly possible to pass through them at LW slack but you will need to keep a very close eye on the depth as there is a 0.4 sounding between Britannia Rock and Cribbin Rock.


Navigation through the Swellies is complicated by the fact that there are numerous islands and rocks situated in what should be the centre of the channel forcing both the tidal stream and yachts to navigate around them.  The main navigation channel is to the South of the Swellies and passes under the eastern span of the Britannia Bridge. This passage is marked by lights, perches and shore marks and should be studied and understood before even starting engines for the passage.  


Here are a couple of videos of the Swellies. The first is a sail through courtesy of Boom Sail Power and Race training






Southbound is easiest as you can depart Puffin island just before the tide turns Southbound and peg a little bit of adverse tide all the way through; you’re looking at an eight mile transit to the Swellies and the HW slack is HW + 2.



Northbound is a little trickier. If you are happy to go through at LW slack (not recommended if you have any serious draft) it’s not too bad but if you are aiming for HW slack you are going to have to go easy on the loud peddle from Fort Balan or you will arrive as the northbound current is still pouring through. Then you must balance your speed through so that you don’t get caught out by the West bound tide which sets in rapidly after it’s turned.




Then, if stopping at Port Dinorwic, and, having worked all that out, you have to factor in the lock only operating HW+ 2hrs.


The Port Dinorwic web site has instructions on the best time to leave them whichever way you are going and don’t forget there is the problem of the Caernarfon Bar to be crossed as well. Click on this link for the navigation over that.



Berthing, Mooring & Anchoring

You would be wise to contact the Harbour Master to tell him you are arriving and find out where he wants to park you. The most probable options will be the Marina Dock on the Strait or the tidal basin inside the lock.  

If you do go through the lock into the Marina it might be a good idea to moor facing outwards because in any sort of a westerly breeze you will have trouble turning her round to get out; whereas it’s not too much trouble to go bows in, send your bow rope ashore and fall back on that into your berth.

The harbour website can be found at      Port Dinorwic | The Marine Group

And a chartlet of the Marina can be found HERE

This opens the Marine Group's Brochure at the relevant pages; just keep scrolling down. If you use the Marine Group's website there is little detailed info for visiting boats and the link to the Brochure is not immediately obvious as the source of the info you need.

An overnight stop here (2022) will cost £3.50 per metre per night

There is also the option of a swinging mooring out in the current at about £20 per night if there is one available. They do have a water taxi for these.


There is shore power (payment by card) and water available in both the outer harbour and the locked harbour. Showers, toilets and laundrette facilities are in the main marina building. The marina can provide both Calor Gas and Camping Gaz.


The marina has a 20 ton hoist and can do winter storage.


For provisioning there is a small Londis/Post Office at the far end of the village


There are some marine boatyard facilities, sailing schools and a riggers which can be found in the business directory

Eating, Drinking & Entertainment

There is a café in the marina, an Italian restaurant just outside.

The Sailing club's website is at http://www.pdsc.org.uk/ 

Port Dinorwic Hotel (just over the bascule bridge) is open to non residents but you would be advised to book 07709 651991.


Your Ratings & Comments

Written by Don Thomson 3 | 7th Sep 2022
No changes apart from tariff.
Written by Don Thomson 3 | 10th Aug 2021
I reviewed these notes in August 2021. Firstly, this marina is now run by the Marina Group along with about half a dozen Welsh Marinas. Their main website covers all these Marinas and unless you download their brochure (which again covers all the Marinas) you will get frustratingly lost. Our link in the Berthing and Mooring section takes you straight to the pages you need in their multi facetted IT. The posh hotel on the hill above the marina is ambiguous as to their attitude to non-residents and enquiries have been made.
Written by Don Thomson | 20th Apr 2018
There are no changes apart from the prices.
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