Lake Minnetonka Targeted Sonar Survey & Underwater Anomaly Assessment

MHM's primary goal for the LMTSS-UAA Project, a Phase 1 archaeological reconnaissance survey, was to determine the nature of specific anomalies?possible shipwrecks & other submerged sites - after conducting targeted sonar scanning of possible anomalies focusing on shallow areas prior to seasonal vegetation growth - exceeded expectations and produced several positive outcomes. Of the 47 unknown anomalies and 2 known wrecks investigated during the Project, MHM and its volunteers accumulated important data about the wrecks and confirmed the existence of 7 new wrecks, 5 new submerged maritime sites, 9 ?other? sites/objects that includes 1 car, 4 trees, 5 big rocks, and 16 false sonar returns. Included in the results are 21 anomalies (A283, A626, A628, A655, A656, A699, A700, A704, A705, A706, A730, A752, A753, A759, A760, A761, A763, A779, A788, A799, A804) that were identified remotely using only sonar since their distinctive signatures relayed enough information to MHM that diving on them was not warranted. These types of determinations - where remote sensing data can be interpreted and trusted to accurately depict anomalies - not only allow for increased efficiency for fieldwork and dive planning but it also increases the workload during finite seasonal archaeological projects. Further, 6 of the 7 new wrecks investigated during the project were discovered in shallow water in areas where seasonal vegetation growth masks acoustical signatures - supporting MHM's contention that targeted re-scanning of shallow areas of Lake Minnetonka produces impressive outcomes. Also, a major positive outcome of this project was the attainment of 4 Minnesota Archaeological Site numbers for 4 wrecks identified from the Office of the State Archaeologist (OSA). In time, the other 3 wrecks will get site numbers once they qualify for that status under OSA guidelines. These wrecks and sites join dozens of other submerged cultural resources already identified in the lake. After the completion of the LMTSS-UAA Project fieldwork in October 2019, there are now 83 identified wrecks on the bottom of Lake Minnetonka or that were once on the bottom, including a Woodland Culture dugout canoe removed from the lake in 1934. Of these wrecks, 53 of them have 52 Minnesota archaeological site numbers; 2 wrecks are features of one site. Further, 4 other types of maritime sites have archaeological site numbers and there are 37 maritime sites or objects without numbers. Additionally, 43 'other' objects have been identified that do not have site numbers, among them 13 vehicles that include 4 snowmobiles, 1 truck, and 8 cars.

Comparing and associating these new sites with known sites increases our understanding of the historical context within which these cultural resources operated or were exploited by Minnesotans. Firstly, the Open Barge Wreck (21-HE-529) not only represents 19th Century transportation, but the commercial waterborne activities associated with bulk cargo carrying. Like the NRHP property the Wayzata Bay Wreck (21-HE-401) - an 85-foot barge owned and operated by J.J. Hill and his partners, and the Half-Decked Barge Wreck (21-HE-505) - the Open Barge Wreck probably transported cut wood and timber from the Upper Lake to Wayzata, transferring the cargo to Great Northern Railway trains headed to the Twin Cities. Beyond this association, the Open Barge Wreck is a tangible example of the skill and knowledge of Minnesota boat builders of the latter 19th Century. MHM contends a probable working life of over 15-25 years is not unreasonable. Like the Wayzata Bay Wreck, Half-Decked Barge Wreck, and the later Hopper Barge Wrecks Site (21-HE-441), 21-HE-529 is a rare example of her kind since work boats like barges were rarely preserved for future generations.

The 1 small wooden plank-built wreck identified during the LMTSS-UAA Project - the Overturned Wooden Scow Wreck (21-HE-531) - joins many other small wooden fishing and hunting boat wrecks preserved on the bottom of Lake Minnetonka, including the Fisherman's Friend Wrecks 1-4 (21-HE-485, 21-HE-489, 21-HE-499, 21-HE-509) and the Flat-Bottomed Rowboat Wreck (21-HE-488). These 5 small wooden wrecks were designed with athwartships bottom hull planking and hard chines; however, the Overturned Wooden Scow Wreck has longitudinal bottom planking and a rounded chine. The combination of attributes - scow ends, rounded chine, and longitudinal bottom planking found in the construction of 21-HE-531 - is unique in known Minnesota small craft wrecks. Further, MHM is unaware of any surviving dry examples of small wooden watercraft in the State with these characteristics.

The history of the sidewheel steamer Minneapolis Wreck(21-HE-403) is well-known and her sinking was contemporarily reported in Twin Cities newspapers. Further, while sport divers have visited the site in previous decades, no comprehensive analysis of the wreck had been completed before the LMTSS-UAA Project. With 3 hours to investigate the wreck by ROV, MHM now understands the wrecking process that produced a complicated, broken-up, partially burned - and truncated from her original size - nautical archaeological site in deep water in Lake Minnetonka. Contrastingly, the gasoline launch Theta Wreck (21-HE-514) is in one piece, in shallow water - and in danger of damage from a variety of sources. The survival of Theta in her complete state on the bottom of Lake Minnetonka greatly enhances Minnesota?s Maritime History - currently she is a one-of-a-kind nautical archaeological site in our State. MHM will consult with the OSA on an acceptable plan to provide Theta's 2 name plates with protection from further damage.

The Steel Row Boat Wreck (21-HE-530) is likely the 2nd earliest example of a small metal wreck so far identified on the bottom of Lake Minnetonka; the earliest wreck is the Steel Motor Boat Wreck (21-HE-510) that sank around 1930. With the possibility that 21-HE-530 may have been constructed by a Minnesota boat-building company, she is an important link in the State?s metal craft production history. While her manufacturer - or home builder - is currently unknown, other Minnesota metal watercraft construction companies represented in Lake Minnetonka include Alumacraft, Larson, Lund, and Crestliner. All 10 small open boat-style metal wrecks - identified to date - on the lake bottom (not including 3 aluminum canoes) were not only produced by various manufacturers or represent home-builds, they are of different models from each other or carry different attributes from each other, supplying great variety in Minnesota's nautical and underwater archaeological records.

MHM has identified and rudimentarily analyzed dozens of wooden wrecks in Minnesota, including Lake Minnetonka. However, none of these wrecks constructed from wood were fabricated using plywood sheets. During the LMTSS-UAA Project, MHM located and identified 2 wrecks with plywood hulls - the Plywood Outboard Wreck (21-HE-528) and the Fiberglassed Plywood Outboard Wreck (Anomaly 764). While building boats with plywood instead of cut planks may suggest inferior construction, the layered nature of wooden sheets glued together - veneers - can produce superior plywood-fabricated watercraft. Additionally, the application of fiberglass onto the plywood hull of Anomaly 764 extended the working life of this small craft since she was built in 1959 (and possibly before that date) and was scuttled around 1976 or 1977, a significant amount of time on the water for a small wooden boat. For Minnesota's maritime history, the identification of 2 plywood wrecks fills in a gap in the corpus of boat types represented by submerged cultural resources in the State.

In shallow water, the Triple Pontoon Wreck (Anomaly 757) is large and obvious when recorded by sonar - when lake vegetation is missing or short - but MHM did not survey the area in 2011 in Spring, but during a time of tall weeds. Therefore, during the LMTSS-UAAProject, it was a pleasant surprise for MHM to record near-photographic sonar images of Anomaly 757 in early May. Diving on the wreck in early June, it was discovered that the wreck, while not only being a pontoon boat, she has 3 pontoons - the first of this design identified by MHM in Minnesota.

The Upright 1986 Chris-Craft 260 Stinger SL LTD Wreck (Anomaly 749) is the first of this brand identified in Lake Minnetonka, and the only the second Chris-Craft recognized on the bottom of a Minnesota lake, the other being in White Bear Lake (the Judge's Boat Wreck). Also, 1 other wreck identified (to date) in Lake Minnetonka falls into the same class as Anomaly 749 - the 1982 Larson Delta Cruiser 7000 Wreck. While the Larson is substantially smaller than the Chris-Craft, she is a fiberglass inboard/outboard fast boat with a cuddy from the 1980s. An obvious attribute of the Anomaly 749 site is her position standing upright in the water column. She joins 3 other Lake Minnetonka wrecks (Alumacraft Model A Wreck, Fiberglass Drag Boat Wreck, Red Fiberglass Wreck), 2 Prior Lake Wrecks (Fiberglass Hydroplane Wreck, Glasspar G-3 Skiboat Wreck), and 2 cars (AMC Rambler and a Chevy) in Medicine Lake that all stand vertically or near vertical in the water column. Submerged cultural resources that stand upright on lake bottoms are uniquely equipped to provide underwater archaeologists with details about sites that are not often accessible - particularly the hull bottom. Also, these sites - in terms of boats with floatation foam or other safety features - prove that vessels with heavy engines and motors will overcome the affect of such preventative measures when faced with a significant leak. In terms of Anomaly 749, while it is interesting to see the molded bottom of the fiberglass hull and its condition, the last several feet of the wreck's stern has attributes that would answer questions MHM still have about the Chris-Craft Stinger 260.

As more Minnesota wrecks are documented, the changes in watercraft design and construction will more completely fill-out the maritime historical record. Many of the smaller craft on the bottom of Lake Minnetonka represent over 140 years of our relationship with historical personal watercraft. When the internal combustion engine began to replace steam-powered boats in the late 19th and early 20th Centuries, watercraft operation by a single person became possible since a boiler operator was no longer necessary. The rapid development of the outboard motor set up the proliferation of personal watercraft, made of wood, steel, aluminum, and fiberglass. The higher speeds attained by internal combustion engines also led to changes in hull design.

Other maritime sites identified during the LMTSS-UAA Project, the Dock Piling Remains (Anomaly 755), Lifeguard Tower (Anomaly 740), Railroad Maintenance Cart (Anomaly 780), Anchor and Rock (Anomaly 805), and the Large Concrete Anchor (Anomaly 809), represent maritime infrastructure linked to the shoreline and large anchorages with unknown purposes. The investigation of 3 objects that may be associated with each other - the Red Metal Object (Anomaly 770), the Metal Rectangular Box and Twisted Piece (Anomaly 771), and the Bench Cushion (Anomaly 798) - has produced more questions as to their identities and purposes than answers. The ~1940 Chevrolet Sedan (Anomaly 778) joins 7 other cars sitting on the lake bottom. One of those cars is nearby Anomaly 778 and both may have been the subjects of a 'Dunk the Clunk' contest fundraiser between the years 1957-1968 (Merriman and Olson 2013, 47-51) Miscellaneous objects such as the Wall Frame (Anomaly 758), Thick Wire Cable and Upright Pipe (Anomaly 482), Barrels (Anomalies 743, 793), and Metal Girders (Anomaly 799) are among dozens of objects blown into the lake by strong storms or deposited there by the habit of disposing of unwanted objects on the ice or dumped from boats.

The diversity of nautical, maritime, and underwater sites so far identified in Lake Minnetonka are tangible examples of the rich maritime history of the area. Through research, diving on wrecks and anomalies to collect pertinent data, and ensuring that the collected information is accessible by the public, MHM will continue to investigate Lake Minnetonka's submerged cultural resources into the future. As shown by the 7 new wrecks identified by MHM during this project, the continued re-scanning of several sections of Lake Minnetonka is warranted. Comparison of sonar data recorded from different directions and various times during the Spring, Summer, and Autumn have revealed new sites, as well as facilitating the recognition of false targets that do not require reconnaissance using SCUBA. This new data allows MHM to produce smart and efficient dive plans; this will continue into the future. The results of the LMTSS-UAA Project summarized above is connected to all the work that came before and that will come after its completion. It is clear that the types of sites that exist in Lake Minnetonka are diverse, archaeologically and historically significant, and worthy of great attention. To date, the watercraft located on the bottom of Lake Minnetonka represent nearly 1,000 years of Minnesota's maritime history and nautical archaeology. In the historic period, the known wrecks represented in the lake span over 140 years of local maritime culture. The data collected during the LMNA-1-9 Projects have been utilized to create the ever-changing Lake Minnetonka Multiple Property Documentation Form, a guide that will be used to nominate Lake Minnetonka's submerged cultural resources to the National Register of Historic Places (NRHP). At this point, the Wayzata Bay Wreck (21-HE-401) has been successfully nominated to the NRHP by MHM. Lastly, the large and significant data produced during the Lake Minnetonka projects has and will be used for comparison purposes as MHM identifies wrecks and maritime resources on the bottom of other Minnesota lakes. To date, these bodes of water include White Bear Lake, Lake Waconia, Prior Lake, Lake Johanna, Medicine Lake, and Lake Pulaski.