Norseman hull - cored or not

[bremin001]

Hi folks, I have a few questions about Norseman hull.

1. My understanding is that the hull is a hand laid molded fiberglass with alternating mat and woven roving (no core). The deck is hand laid fiberglass cored with end grain balsa.

There are two reason for this question:

a) this post suggests that the hull is cored with airex foam, which I don't think was even used in 1984: https://www.yachtworld.com/yacht/198...n-447-9002151/

b) the boat I am interested appears to has a survey suggesting the following:
"areas of altered sounding were present:
• Under the galley near the sink outlet skin fitting.
• An area of approximately 600mm x 450mm below the generator.
• A small area under the aft cabin lockers Portside.

All these areas are related to the hull. If hull is a thick fiberglass w/o core, would this suggest areas of delamination? I've never heard the thick, old, all fiberglass hull to delaminate like this. If not delamination what else can it be?

2. My understanding is that the keel is lead, fully encapsulated in the keel with no bolts. However I see some boats that suggest that keel is a lead bulb (attached with bolts to the bottom of the boat) - did they make both versions?

Thank you,
B

[boatpoker]

Originally Posted by bremin001

All these areas are related to the hull. If hull is a thick fiberglass w/o core, would this suggest areas of delamination? I've never heard the thick, old, all fiberglass hull to delaminate like this. If not delamination what else can it be?

I've never surveyed a Norseman so I cannot confirm type of hull coring if any however. delamination of solid FRP hulls while unusual is not unknown. Without personal examination and sounding I cannot give a determinant answer. Improperly mixed or improperly cured polyester resin or the use orthopthalic resins (cheap resins) or an excess of chopped mat can invite hydrolysis Which in turn can lead to delamination. Osmosis testing in boats

[GordMay]

Structural foam cores have been manufactured, for at least 75 years [1950s], from a number of thermoset and thermoplastic polymers, including: polyvinyl chloride [PVC], polyurethane [PU], polystyrene [PS], styrene acrylonitrile [SAN], polyetherimide [PEI], and polymethacrylimide [PMI]. Of the various structural foam core types, perhaps the most commonly used is PVC [crosslinked or linear], which is actually a hybrid of PVC and polyurea.

AIREX® foams [they make many] are rigid foams, based on various polymers*, manufactured by 3A Composites Group [part of Schweiter Technologies].

* AIREX C70, often used in boat hulls/structures, is a closed cell, cross-linked PVC polymer foam.
➥ https://www.3accorematerials.com/upl...-ex-Europe.pdf
➥ https://www.3accorematerials.com/upl...-ex-Europe.pdf

“Foam Core Materials in the Marine Industry” ~ by Trevor Gundberg, Composite Materials Engineer with DIAB Inc.

"... The first foam material specifically formulated for a marine environment was a poly vinyl chloride (PVC) and isocyanate blend (simply called PVC foam) created in Germany by Dr. Lindemann in the late 1930's and 40's. It has been rumored that this early version of PVC foam was used in the German E-boats and even in the famous 'Bismarck' battleship..."

➥ https://www.boatdesign.net/articles/foam-core/

[Bycrick]

If you’re talking about the Norseman 447 sold from Marina del Rey, I was told by the surveyor in MDR, that they were built in three hull versions, no core, balsa core, airex core. He said that I was lucky to have the solid hull. I think all the decks were balsa cored.