Assessing Older Boston Whaler Boat Hulls Prior to Purchasing

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Assessing Older Boston Whaler Boat Hulls Prior to Purchasing

Postby jimh » Wed Oct 05, 2022 10:40 am

Many buyers are considering older Boston Whaler boats, and those hulls can be in a wide range of condition. This article summarizes a few areas that buyers should investigate when considering the purchase of an older Boston Whaler boat.

Gel Coat Condition
Older boats which have been neglected often exhibit cracking or crazing in the gel coat layer of their hulls. Cracks of this type are usually due to neglect and from having continual exposure to sunlight and weather. If the cracking is extensive, repair of individual cracks will be very labor intensive. Often the gel coat layer of boats in this condition will be abraded away to get to a firmer layer, and the entire hull or deck will be refinished. Because spraying gel coat resin is typically a difficult process for most do-it-yourself repairers, the new finish will probably be paint.

Another common defect in the gel coat is stress cracking. Stress cracks tend to occur in areas where the gel coat layer may be thicker than usual, and where there is some stress or potential for movement. Some stress cracking seems inevitable in older boats that have had years of use. Stress cracking should be investigated to see if there is any looseness or movement in the hull in that area.

The FAQ gives advice on making hull repairs. See

Q5: how is damage to a Unibond hull repaired?

Water in the hull
Concern about a Unibond hull retaining water is a very common worry and is quite justifiable. Many older boats--again, particularly older and neglected boats--may have acquired water in the foam interior. Among the frequently asked questions, this is perhaps the oldest one. See the FAQ at

Q3: Is there water in a Unibond hull?

Fuel Tank Integrity
For Unibond hull boats with below deck fuel tanks, the typical situation on older boats will be an aluminum fuel tank with a surround of foam. If the fuel tank and surrounding foam have been subject to continual inflow of water and are believed to be chronically wet, there is very proper concern about the integrity of the fuel tank walls. The most simple test is a sniff test: generally the presence of any gasoline outside the tank itself can be detected by a human nose. A wet surface on the tank surrounding foam is a sign of possible problems.

Another element of the fuel system that needs careful review is the state of the rubber fuel hoses. On hulls made before c.1987, the rubber hoses may not be tolerant of any alcohol-gasoline blended fuels. Also, a rubber fuel hose does not last forever.

Brass Through-hull Drains
Another very common defect found in older boats is a a brass through-hull drain that has deteriorated, with the brass corroded away. Failure of the brass tube or failure of the seals at either end of the tube will allow water to come into contact with the foam interior of a Unibond hull. Again, the FAQ has advice on this topic at

Q12: How Are brass drain tubes replaced?

Wavy Hull Sides and Osmotic Blistering
Two more defects seen in older Unibond hulls are wavy hull sides and osmotic blistering. Wavy hull sides have occurred in a few production epochs of Boston Whaler boat construction, but generally the factory took action in severe cases and replaced the hulls. Some minor waviness in the hull side is an unfortunate cosmetic defect, but is probably not evidence of a serious internal problem in a Unibond hull. The FAQ comments on this at

Q10: is a wavy hullside a problem?

Osmotic blistering is a problem that occurs in many fiberglass boats constructed with polyester resins which have a history of very long immersion in water. This problem was more prominent in the 1980's than today. Boston Whaler has long advised that the immersed portions of their hulls need to be protected by a barrier coat and an anti-fouling coat. For more about how osmotic blistering occurs, see this interesting paper of the topic:

The Cause of Hull Blisters ... isters.pdf

Defects in Wood Components
Generally the wood used in a Boston Whaler boat that will be exposed to weather is very high-quality marine hardwoods such as teak and mahogany. But even these fine woods are subject to rot in freshwater if their surfaces are not protected by oil or vanish or epoxy finishes. Internal wood reinforcements, particularly at the transom, are typically plywood. Evidence of poor seals on the engine mounting bolts or on another fasteners screwed into the transom is a concern, especially on a freshwater boat.

Buyer Inspections
Sellers of boats will be reluctant to allow a prospective buyer to make any sort of invasive test of the hull, such as drilling a small hole in the transom to see if water appears. Establishing if a Unibond hull holds water will have to be done by non-evasive measures prior to purchase.

Ultimately, anyone looking at a Boston Whaler boat in poor condition that has
  • badly cracked and crazed gel coat
  • shows evidence of water in the hull
  • has a suspicious fuel tank
  • has corroded or missing brass through-hull drains
  • has osmotic blistering
  • has wavy hull sides, and
  • has rotted wood
may want to think carefully about purchasing and older Boston Whaler boat in such poor condition.

As readers may have noticed, this article makes several references to the Frequently Asked Questions article in the REFERENCE section. For anyone who is new to Boston Whaler boats, I strongly recommend reading the entire FAQ and any other articles linked to in the FAQ.