Scott, this is further to your experience and ability to read water from your river paddling trips:
Since many people paddle there, many beginners or less experienced on the ocean, I am going to have a go at explaining what I have come to know about paddling conditions in the San Juan Islands over the course of my long experience paddling there. I have often compared Ocean paddling versus river paddling to sport climbing vs mountaineering. Many similar techniques and skills, totally different environment and hazard profile. Others may also have comments, or additional ideas to add I hope.
The northern tip of Lummia Island, Sucia, Matia and Patos as well as the northern side of Orcas all border on Boundary Pass. On the other side of the pass is Saturna Island where you will find East Point, Tumbo Island and Boiling Reef. It is a little better than 5kms from Patos Island to Tumbo Island or East Point on Saturna. People who are paddling the inside passage route from the Washington to Alaska have to cross the pass. The place to do this if going north is from the north Side of Stuart Island to Bedwell Harbour on South Pender where you can clear Canada Customs. Going South, the shortest option is likely from a campsite on Gooch Island to the US Customs Station at Roche Harbour on the Northern end of San Juan Island, a distance of about 11 kms, almost 7 miles. That crossing is at the junction of Harrow Straight and Boundary Pass. That crossing can be an interesting ride, even on the ferry to Anacortes if you like to watch water, especially if you are on the water when a "spring tide"
I will also note that English names for places in this area sometimes note a significant geographic or hydraulic feature: Obstruction Island, the Haystacks, Boiling Reef, etc. Such descriptive naming by Europeans seems to be significant, in that we usually prefer to name places after persons. This whole area is prone to rips, overfalls and high winds. If you look at the hydrographic chart
for the area, you can see that the water in the straight and the pass are deep, but narrow and constricted by the San Juan Islands as well as the Olympic Peninsula, the Whatcom County Mainland the Islands of Skagit and Snohomish Counties, and on the Canadian side by the Southern Gulf Islands and Vancouver Island. The underwater topography is in a word constricted, or in another word convoluted. The topography above water equally so, more on this in a bit
Using your river paddling experience as an analogy think currents and a constricted passage, only with multiple channels. To add to the unique tidal characteristics of this group of Islands, on a flood tide, the currents empty out of the Straight of Juan De Fuca into Georgia Straight to the North and Puget Sound to the South. The Straight of Juan De Fuca itself, was documented by the early Spanish and British Explorers to be a very scary and dangerous place in their sailing ships. It can still be a dangerous and scary place for small craft, even with engines, weather reports and technological navigation aids. Obviously on the ebb the reverse is true.
Think of how much water is going back and forth through the San Juan Islands at both flood and ebb tides. The amount of tidal flow makes the Missisippi, or the Amazon Rivers look like trickles. And, it reverses every single day with the added complexity of tidal fluctuations, spring to neap tides and back again monthly. Think agitator in a washing machine during strong tidal flows as an analogy for the islands during this discussion. When you are sitting on top of all this water in good conditions, it can all seem rather lake like. That makes it very dangerous for beginners and even experienced paddlers like you who do not understand, or who have not considered all this. I have paddled between Lummi Island and Matia, or Clark Islands when it was a huge Mill Pond, glass! I have also paddled this when a strong spring tide was creating huge rips between Clark, Matia and Orcas, as well as impressive and dangerous rips and over falls from Village Point on the West side of Lummi, north into Boundary Pass.
Now on to the other factors, above ground topography that adds to the complexity and unpredictability for small craft in these islands, and wind. If you look at the wind patterns, I like this site, "WINDY"
as a visual for this purpose. You can see that the San Juan Islands are the nexus, not just for strong tides, but for the winds funnelling down the Straight of Juan De Fuca, and sometimes, out of the north from the Straight of Georgia, and frequently out of the South and Southwest. You can see in the image, that both the Canadian Gulf Islands and the North end of Puget Sound are most often in a wind shadow. This is most often the case for those areas, unless there are strong winds from the north or more frequently from the south or southwest. I have paddled in calm conditions in the Canadian Gulf Islands when the wind was raging in parts of the San Juans.
Topography, Mount Constitution is a mountain on Orcas Island, the highest point in the San Juan Islands and the second highest mountain on an ocean island in the contiguous 48 states. Only Devils Peak in the Channel Islands of California is higher. Mount Constitution is 731 meters, (2400 feet) high. You have similar, though lower heights on Lummi Island, Cypress Island, Saturna Island and Blakely Island at the norhtern and eastern sides of this group. These high islands act like rocks in the "wind river" that flows around and through the San Jauns. Simplified explanation, the San Juan Islands obstruct and disrupt both huge tidal flows as well as what are often strong winds, There are not infrequent storms where ferry service to Lummi Island and also to the San Juan Islands has to be cancelled, though that is at the extreme end. While winds lessen to a degree in summer, they can still pick up quickly, especially when there is a pressure change.
For anyone choosing to paddle the inside passage route, the crossings to and from the San Juans to the Southern Gulf Islands are one of the four "crux" areas of the trip. The others are the tidal rapids in the islands between Georgia and Johnstone Straights, the open ocean 40 km crossing from Vancouver Island past Cape Caution to the inside passage behind Calvert Island and the crossing of Dixon Entrance near Prince Rupert to Alaska. Though I have not paddled the entire route myself.
To end this lengthy dissertation on the San Jaun Islands, their tides and currents, I will say that they are my home paddling grounds, even though I am Canadian. I have learned more about tides and tide/wind interaction as it affects kayaking there than anywhere else. It is a wonderful place to paddle, but it deserves respect and caution, especially if you do not understand, or are unaware of what I have set out in this post. It has taken me almost 40 years of paddling and quite a few tense crossings there, even with my current knowledge and experience to reach my current level of understanding. Even Hale Passage, narrow and seemingly protected as it is, can be a very dangerous place. I like visuals, so here is one more link, an article and a video of the Whatcom Chief
crossing from Gooseberry Point to Lummi Island in a November gale.
Back in 1997, Matt Broze published a book called "Deep Trouble: True Stories and Their Lessons From Sea Kayaker Magazine"
. Well worth reading. Many of the stories he relates took place in the San Juan Islands. A good read for anyone wishing to get their head in the correct place for paddling more exposed and complex waters and needing instruction on ocean kayaking hazards.
Once in a while, it is good to put, perhaps useful experience, and knowledge in writing, and to share it. Live and learn. Just say'in!