A new engineering evaluation of Spring Point Ledge Lighthouse in South Portland has laid out significant challenges for the Trust that owns it. The lighthouse, which celebrated its 117th birthday in 2014, is located at the end of a breakwater at Fort Preble on the campus of Southern Maine Community College.
The study, conducted by Becker Structural Engineers of Portland, Maine, with assistance from Gredell & Associates of Newark, Delaware, and Ocean Technical Services of League City, Texas, included a visual inspection of the lighthouse and an ultrasonic inspection of the lower caisson to evaluate the tower’s structural integrity and allow the Trust to set priorities for the maintenance and preservation of the iconic lighthouse. Grants from the Davis Family Foundation and the Morton-Kelly Charitable Trust funded the study.
While the report acknowledges the lighthouse is in generally good repair, it expressed concern about the deterioration of the lower portion of the caisson, particularly in the inter-tidal zone between high and low tide. Breaches in the flanges between the cast iron plates that make up the exterior of the caisson have allowed water to enter and weaken the integrity of the cement that fills the bottom thirty feet of the caisson. The condition of the caisson below mean low water is likewise unknown, since the portion of the structure surrounded by the breakwater is not accessible for inspection. The ultrasonic inspection of the 1-1/2 inch thick cast iron plates forming the accessible part of the upper caisson revealed loss of plate thickness as high as 60 percent, with the average being around 30 percent. Loss of too much plate integrity could require replacement, an expensive and difficult process since few mills today produce cast iron sheets.
Paul Becker, of Becker Structural Engineers, presented the Trust with two alternatives to determine the condition of the lower caisson. The best option, costing an estimated $80,000, involves removing the breakwater rocks adjacent to the caisson in two locations and drilling several core samples through the cast iron plates and into the cement within to determine the location and extent of any voids that may have been formed between the plates and the cement. A less effective, but less expensive, option is to create an opening in the caisson and attempt to insert an inspection camera inside for a visual inspection. This alternative method is estimated to cost approximately $25,000.
Trust chairman Keith Thompson said “Maintaining and preserving a lighthouse in a highly-corrosive salt-water environment is not for the faint of heart. Corrosion is taking place every minute of every day. It never stops. The challenge for the Trust is to raise funds through grants and donations to take action now to stop any further deterioration.” Thompson noted that historical records indicate the problems with the lower caisson are not new. The Lighthouse Board was forced to repair the caisson and place steel bands around it in 1912 and again in 1929. The upper band is no longer effective and it is assumed by the engineers that the condition of the lower bands is “poor. “The initial estimates are just to determine the extent of the damage to the caisson,” said Thompson. “The engineers will then have to develop a plan to effect repairs and stop any further damage.”
The study estimates approximately $180,000 will be required to make all repairs recommended by the study, an amount that does not include costs to remove some rocks from around the lighthouse, repair and reinforce the caisson, and replace the rocks. Total costs could well exceed $300,000 to $500,000.
The Spring Point Ledge Light Trust opens the lighthouse to the public on weekends during the summer and Becker emphasized that the slow deterioration of the caisson poses no immediate threat to the safety of the structure.
“Entrance fees and other sales during the summer are the primary sources of revenues for the Trust, an all-volunteer non-profit organization, Thompson said. “The funds required to accomplish these repairs are beyond the amounts generally granted by any single charitable foundation and well beyond what the Trust can raise on its own. We anticipate that multiple grants or substantial donations will be required to accomplish the necessary repairs in stages, with the caisson being the most critical.”
The Trust notes it would be a shame to allow the deterioration to continue to the point where the lighthouse is no longer safe to open to the public. In both 2013 and 2014 over 3,500 people toured the lighthouse.
A copy of the report may be downloaded here.
The Spring Point Ledge Light Trust is a 501(c)(3) non-profit organization that owns the Spring Point Ledge Lighthouse. The lighthouse was transferred to the Trust in 1998 under the Maine Lights Program. The Trust is composed entirely of volunteer Trustees and receives no money from state, federal, or local governments.