Causes of soft spots

I have a 1984 H-18 that currently has no soft spots. What causes soft spots and how do you prevent them?

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Jeff Serene
1984 Hobie 18 Magnum
Phoenix, AZ

Hi Jeff, Normally, a soft spot is caused when the foam beneath the fiberglass deck gets compressed. The fiberglass usually pops back into place but the foam remains compressed. Soft spots can be caused several ways. The most common is body weight being bounced up & down in the same spot. On an 18 the usual place this can happen is just forward of the rear crossbar. It's rare to get a soft spot forward of the dagger board well. The best advice I can give on preventing a soft spot is to sit on the tramp whenever you can. I usually sat on the deck though, midway between the well and the rear crossbar...but I sat...didn't bounce up and down. Another way to get a soft spot is by something being dropped on the deck, like the mast, a tree branch (yep it happens) or even a heavy ice chest. When this happens though, the soft or spongy feel of the deck may be due to the internal layers of fiberglass being cracked. When someone on your boat wants to stand up to walk around, or when you're getting ready to land at a boat dock or the beach, have the person walk on the textured non-skid and not on the center of the deck. The edges of the 18 deck are stronger than the center.

Fat boys sailing old boats!!!

The sun breaks down the foam over time and water breaks down the resin a bit and fat guys with boney butts sit on the same spot over and over again, "friends" walk up and down the bows, Kids think its fun to jump on dads boat on the beach or water and presto-soft spots.

Best solution, buy a new/newer boat, cover it when not is use, don't walk on it, jump on it, or sit on it. Ok, sit on it, but do so softly...

careful some on the forum consider this flaming and trolling.

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Bodhisatfa

Sit, don't plop. Knees on the hulls also can concentrate weight.

Interesting replys. Most soft spots come from water intrusion between the glass. The foam absorbs the water and holds it, cold freezes the water expanding it and tearing the glass from the foam. Heat turns the water into vapor which expands between the layers and same result. Once the delam between the glass and foam starts it will continue to zipper apart.
Thats the correct answer. Impact will create small soft spots but typically the small impact cracks the glass allowing water in which creates the problem.

How's this...

Exterior glass skin heats and expands at a faster rate than the foam and the inner skin and after ten-thousand cycles the bond finally breaks down. Foam used in the 'redlines' and newer boats allows the resin to penetrate and adhere better. I could be full of it, but that's my story.
It always develops first where the hull is exposed to max sun and at the widest, unstructured spot on the deck... also this is where people stand, but that just physically separates a bond that has already failed. My theory is that boats in hot climates, especially left uncovered in direct sun are most susceptible to delam. I think if you left a brand new boat in the direct sun in AZ for 30 years and never sailed it, then went and stood up on the deck it would delaminate. Also, I think colored boats delam more than white due to heat absorption. Some boats just had better lay up and bonded better.

What do you think?

J

Also, how about the stress of sailing? The bows are torqued inwards and upwards repeatedly... let alone stresses caused by the wave action.

We do know that the foam used now is far better than what was used back in the 70's - early 80's. The lamination processes have also been improved. Don't see the delamination issue that often these days... if ever.

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Matt Miller
Former - Director of Parts and Accessory Sales
Warranty and Technical Support
Hobie Cat USA
(Retired 11/7/2022)

I don't know Jeremy, good points to be sure. The most recent repair I attempted was on a '84 18. The boat still had original gelcoat on the keels, sails are like new Catfevers. The black aluminum was turning clear from the time in the sun and the tramp was of course rotted. This boat had been left nose down on the trailer for god knows how long. It had no delam or soft spots on the deck anywhere but the sides of both bows were soft all the way to the crossbar. It was an impossible repair, pumped 3 gals of West into those hulls and it just kept coming back apart. Keeping the boat covered and dry on the inside is critical to long life.

I don't know about sailing pressures creating soft spots but am sure it could be a culprit. My old '82 18 was sailed very hard for many years in the ocean, until 2000. She tore the topcap loose from the hulls at the rear crossbar, which was repaired with portholes behind the crossbar. She had only one softspot in the deck, right where the skipper sits. This spot was originally a knee ding looking area, circular crack. Over many years the crack took in water and when hot would push the water out. The spot was repaired a few months before she got t-boned at a race and was taken out of service. Great boat that gave lots of memories, I love the H18!