YMS Minesweeper Deck Plans

Located in Lake Washington are three YMS minesweepers.  Two of these vessels are very much intact.  Our team has been using the below deck plans to explore these three vessels over the last several years.  These deck plans are for YMS series 135-409.

Please note that these plans should be used only for general reference.  The vessels in Lake Washington have been modified following their military use and do not fully match the structural diagrams.  Additionally, the two groups conducting penetration dives on the newest minesweeper both experienced partial structural collapse.  The latest collapse was quite serious and could easily have been life threatening.   Both dives required a zero visibility exit from the vessel.

Penetration dives on the Lake Washington Minesweepers should not be undertaken.

The below files are high resolution PDF files:

Outboard Profile

Inboard Profile & Deck Plans

Main Deck, Forecastle, Chart House & Pilot House

Identity of newest Minesweeper narrowed.

Over the last 10 months Puget Sound Divers has conducted a long series of exploration dives on the shipwreck labeled Minesweeper #3. Evaluation of this vessel began with side scan imagery followed by external survey and documentation. Once complete a series of penetration dives was conducted with most all below deck and superstructure areas explored. Despite the extensive survey clear and definitive identification had not been determined. Our research was presented to David Shirlaw an expert in maritime history and with David’s help our work was sent to historians worldwide.


Side scan image of YMS #3 - Now identified as either YMS 118, 124, or 311.

Dr. William Lafferty of Wright State University was able to confirm the identity of YMS#1 as the former research vessel “Healys #1” (Ex-YMS 416) and narrow the identity of YMS #3 to either YMS 118, 124, or 311. While information does exist in the public domain regarding the fate of some of these vessels the validity of some accounts has not been substantiated.

Recently, our work was published in SeaWaves Magazine along with side scan imagery of the YMS 416.

Penetration Dive on the Shipwreck of Minesweeper YMS #3

Shaun Gardner and Ben Griner dove on the shipwreck of a YMS class minesweeper sitting upright in 205 feet fresh water in Lake Washington. Our team calls this wreck YMS #3 as it has not been identified at this time. We have been diving this wreck for several months now looking for identifying markings without much luck.

Shaun dropping below deck through floor hatch

ShaunDroppingBelowDeck.gifToday Shaun and I entered the main deck through a side door exploring both forward and aft. Penetration lines were run by Shaun and secured tightly, low and to the side of our travel. The team entered with two decompression bottles each and I advanced a video and lighting system. The HD cameras have proven very helpful as they are able to see through the silt and percolation far better than the divers. Upon finishing the survey of the main deck visibility remained between 1-2 feet which is expected for wrecks in this lake. Shaun squeezed through a floor hatch to begin exploration of a lower deck. While Shaun was tying in the penetration line a section of steel support collapsed and briefly pinning me over the hatch area and Shaun’s only exit.


Visibility after 8 min of penetration

Not knowing how large the section of ceiling was falling I quickly scrambled and got one leg free and used it to drag my other leg free. Obviously visibility dropped to zero and we ended the dive exiting using touch contact and following the penetration line. The debris fell on part of the penetration line but we easily picked it up again.



Visibility after partial collapse 

Despite a less than desirable penetration we had a comfortable and uneventful decompression.  Tim Evans and Marc Greenway acted as captain and surface support for this dive. 

Side scan imagery of the newest YMS minesweeper in Lake Washington.

The image below is of the third minesweeper in Lake Washington and currently called YMS #3 by our team as we do not know it’s true identity. The goal of this image was to cast a shadow of the ship not necessarily look at the ship itself.

YMS3-ColorSideProfile2008-.gifNote the highly detailed shadow showing that this vessel remains intact and giving an excellent representation of physical structure.


Side scan imagery of the YMS Minesweeper #3 in Lake Washington.

Below is a new image of the third Minesweeper in Lake Washington.  This image was taken on a 60’ scan with the tow fish passed directly beside the vessel.  You can see the open holds and equipment on deck.  The curved shape to the vessel was caused by a speed change and slight angle change of the side scan sonar.  In this image we let the wind push us pass the shipwreck without any power from the boat.


Wreck dive on the YMS #3 Minesweeper

This Saturday our team dove on the YMS #3 Minesweeper. The conditions were about perfect for this dive with a calm surface. Ben Griner and Shaun Gardner descended to 200’ and tied the drop line into the wreck. A total of 30 minutes was spent on this shipwreck with exploration priority defined prior to the dive. Despite several dives on this shipwreck identifying markings have yet to be found. The stern deck was explored first with evaluation of one open hold for equipment. YMS3-60feetTwoScreensCrop.gifA second hold was not explored on this dive due to excessive free floating line. We will plan penetration of this area on a later dive. Using care to work around fishing net draped over the cabin structure and partially blocking a primary entry point the team explored the cabin area as well as some second deck rooms. Several items were noted for future exploration for identifying markers. On this dive examination of several equipment items was a priority. A generator contained several intact metal labels however; we were unable to gain enough information to assist with narrowing the equipment to a specific vessel.

Greg Wilson graciously volunteered to be our safety diver on this dive. On the surface Scott Christopher acted as captain. In all, the dive was successful. Ben experienced as failed dry glove and experienced some flooding but stayed reasonable warm. Total dive time was just shy of 80 minutes and temperature at depth was 42 degrees.

Higher Speed Side Scan Pass wreck of Mine Sweeper Lake Washington

This weekend members of Puget Sound Divers tested a new software package promising to allow for greater sensitivity at higher scan speeds, longer scan ranges, and silted water conditions. Below is a scan of the YMS #3 at distances of 400' and 600' with boat speeds of 4.5 mph. One pass was taken perpendicular and one pass parallel to shipwreck of the Minesweeper YMS #3. This vessel is approximately 135’ long and generally gives an excellent image by side scan sonar. YMS3HighSpeedPass200-600wit.gif


These images are about what we were expecting.

Miserable weather makes exploration challenging on Lake Washington.

Yesterday Puget Sound Divers hit the water in an attempt a dive on the shipwreck of Minesweeper YMS #3. After waiting for a wind break and predicted 12 hours of calm the team headed out.

MarcWaiting.gifMarc Greenway - waiting for a break in the weather.

ShaunMoreCoffee.gif Shaun hasn't has his coffee yet.  If he only knew how exiciting his day as captain would be.

Unfortunately, surface conditions did not improve in the wind sensitive location of the YMS #3. After hovering over the site for more than an hour the team moved south down the lake to attempt some side scan imaging while waiting for a wind break.

Weather3.gif Maybe we should have waited longer!

Several new images were obtained of previously identified potential targets however, attempts to improve imagery and shadowing of YMS #3 was not to be. The images obtained were all of poor quality and do not show the details we were hoping for.

Stay tuned for a series of side scan images to be posted later.


Puget Sound Divers discovers third minesweeper in Lake Washington

This new mine sweeper titled YMS #3 was initially discovered by Puget Sound Divers in June of 2007. This is truly an amazing find and is the most intact of all the known Minesweepers in Lake Washington. A significant amount of equipment remains on this vessel as does nearly the entire bridge structure and upper decking.


300px-Yms324.pngSeveral opportunities exist for penetration and exploration on this vessel. Last month SCRET announced that they recently independently found this same minesweeper. With on-going exploration now being conducted by two independent teams it is hopeful that the identity of this ship will soon be determined.