Everyone says “Grummans last forever” and I’ve paddled enough of them to know they’re tough. But “forever” gets thrown around like data, and I’m not seeing much beyond anecdotes. Before I drop money on another 17’ double-ender for mixed fresh/brackish use, I want hard info, not nostalgia.
Here’s what I’m challenging and what I’m looking for from people who’ve actually tested, repaired, or fleet-managed these:
Alloy/temper and thickness by era: Did Grumman change alloy or temper over the decades (e.g., 5052-H3x vs 6061) or skin thickness (.040 vs .050) on 15/17/19 models? Anyone done hardness tests, spark/chem analysis, or ultrasonic thickness mapping on older vs newer hulls?
Work hardening and fatigue: After decades of flex, especially around ribs and the keel seam, do these hulls get measurably stiffer/brittle? Has anyone done dye-penetrant or eddy-current inspections around rivets and stems and found crack initiation rates?
Rivets and sealants: What rivets did Grumman actually use (solid vs blind, alloy) and what sealant was used on the lap seams/keel? If you’ve re-bucked or replaced rivets, what worked long-term in real use? 5200 vs 4200 vs polysulfide vs butyl, and did you use Duralac or similar to prevent crevice/galvanic corrosion?
Galvanic traps: I keep seeing seat/thwart retrofits with stainless bolts into bare aluminum. Anyone logged multi-year outcomes in brackish or road-salt environments? Pitting under gunwales, at seat brackets, or under the keel extrusion? Data beats “should be fine.”
Foam flotation age-out: End-cap foam on older hulls… waterlogged? Crumbling? Anyone weighed their canoe dry vs after a week afloat to quantify absorption? Best modern replacement foam and attachment that won’t set up corrosion cells?
Noise reality check: The “aluminum spooks fish” line-has anyone measured in-water sound with a hydrophone comparing aluminum vs plastic/laminate under identical taps? Any proven damping mods (alubutyl, cork, rib inserts) that reduce structure-borne noise without trapping moisture or adding silly weight?
Keel dogma: The external keel gets credited for tracking and blamed for drag/snag. Has anyone A/B tested identical hulls with and without the keel (or a low-profile replacement) for tracking, efficiency, and crosswind behavior? Not theory-GPS tracks/power vs speed or timed runs.
Stiffness testing at home: Simple, reproducible midships deflection under a known load would be useful. Anybody built a jig and recorded deflection over time to quantify oil-canning progression after, say, a rocky season?
Salt and storage: Long-term brackish/salt use-what’s the actual maintenance cycle to avoid crevice corrosion under lap joints? Rinse routines that matter, sacrificial anodes on a canoe (crazy or reasonable?), and storage practices that demonstrably reduce corrosion.
Finish myths: Polishing vs leaving patina. Does regular polishing measurably increase corrosion by stripping oxide, or does it actually help by removing chlorides? Anyone tried chromate conversion (Alodine) or clear coat and tracked results?
Structural red flags: Common failure points you’ve seen on older Grummans-stem castings, thwarts, rib terminations, transom on Sportboats-what fails first and when? Photos and timelines beat “never seen it.”
Economics without romance: With current used prices, does a tired Grumman still beat a T-formex or triple-dump poly hull over 10 years for livery/camp duty once you include rivet work and leak-chasing? Fleet managers: what’s your cost-per-boat-year across materials?
If you’ve got data, please share specifics:
- Model/length/year (approx)
- Environment (fresh, brackish, salt), storage
- Measured thickness/hardness if any
- Rivet/sealant work done and years until next intervention
- Weight before/after re-foam, and any buoyancy test results
- Noise measurements or at least controlled A/B notes
- Photos of corrosion/cracks with location notes
I’m not anti-Grumman; I just want to separate legend from physics. If the answer is “they’re great, but do X, Y, and Z every five years,” that’s useful. If the answer is “old ones were .050 and shrug off abuse; new ones aren’t the same,” also useful-but show your work.