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Search: Posts Made By: MikeJohns
Forum: Sailboat Design and Construction   1 Week Ago
Replies: 811
Views: 31,920
Posted By MikeJohns
Re: Steel vs Fiberglass

This is a good example.
It's precisely what happened in the BS marketing hype about one of his designs T boning a barge (at hull speed no less).

Witnesses to the event said the boat was...
Forum: Sailboat Design and Construction   2 Weeks Ago
Replies: 811
Views: 31,920
Posted By MikeJohns
Re: Steel vs Fiberglass

Jeff
I had a client 4 years ago who wanted his steel Wittholz altered below the waterline, I designed a fin keel and balanced double hung rudder to replace the shoal draft full keel and transom hung...
Forum: Sailboat Design and Construction   3 Weeks Ago
Replies: 811
Views: 31,920
Posted By MikeJohns
Re: Steel vs Fiberglass

He doesn't like any quality strength or construction standards because he disregards them all. But he's referring to ABS OSRY and Lloyds being the pertinent standards of his day. Now replaced with...
Forum: Sailboat Design and Construction   3 Weeks Ago
Replies: 811
Views: 31,920
Posted By MikeJohns
Re: Steel vs Fiberglass

Attached are some of the more extreme events where steel boats remained intact and afloat. The 1st two yachts were hit by ships. A terrifying aerial assault by a whale off Cape Town. And a dent from...
Forum: Sailboat Design and Construction   3 Weeks Ago
Replies: 811
Views: 31,920
Posted By MikeJohns
Re: Steel vs Fiberglass

You cannot see it but all materials have an elastic response to a load. The hull plate does flex, the shrouds do stretch, the hull wracks, twists hogs and sags and the stresses should all flow nicely...
Forum: Sailboat Design and Construction   3 Weeks Ago
Replies: 811
Views: 31,920
Posted By MikeJohns
Re: Steel vs Fiberglass

That's getting better but you are still using Ultimate tensile strength rather than yield :-)

But you are making too many assumptions without being able to show that they are valid. The load is...
Forum: Sailboat Design and Construction   3 Weeks Ago
Replies: 811
Views: 31,920
Posted By MikeJohns
Re: Steel vs Fiberglass

Brent
That's another straw man that you have invented. Again you are avoiding the real issue; the compression post landing directly on the hull plate.
That is not a tensile strength calculation,...
Forum: Sailboat Design and Construction   4 Weeks Ago
Replies: 811
Views: 31,920
Posted By MikeJohns
Re: Steel vs Fiberglass

The mylar ruler was for you to try to teach you about contraflexure and stress transfer. Its actually interesting and pertinent to your design.

As you know, I went to some effort modelling one of...
Forum: Sailboat Design and Construction   4 Weeks Ago
Replies: 811
Views: 31,920
Posted By MikeJohns
Re: Steel vs Fiberglass

That's invalid. Again.....

The pertinent fact is that the compression post in your design lands on the hull plate, next to a chine which is immaterial. It still lands on the hull plate with no...
Forum: Sailboat Design and Construction   4 Weeks Ago
Replies: 811
Views: 31,920
Posted By MikeJohns
Re: Steel vs Fiberglass

Tom ( a metalworker/welder by trade) had already added significant framing to the hull that wasn't specified by Brent. Tom thought it was required, and added it.
Then Tom had questioned Brent over...
Forum: Sailboat Design and Construction   4 Weeks Ago
Replies: 811
Views: 31,920
Posted By MikeJohns
Re: Steel vs Fiberglass

Brent gets a wee bit confused with engineering numbers and Naval Architecture concepts both. He'll post the same argument every time no matter how gently people tell him he's off base by a country...
Forum: Sailboat Design and Construction   4 Weeks Ago
Replies: 811
Views: 31,920
Posted By MikeJohns
Re: Steel vs Fiberglass

Bob
I don't know Jim Betts, is he a composites tech guru?

I said I saw it specified recently, I thought I'd made it clear I wasn't enamored by it. I think the idea of the Kevlar is to add...
Forum: Sailboat Design and Construction   4 Weeks Ago
Replies: 811
Views: 31,920
Posted By MikeJohns
Re: Steel vs Fiberglass

CF is much better than any GRP based solution no matter what they try and reinforce it with. I just thought you might be interested to know was all.

CF has a fatigue limit just like steel does....
Forum: Sailboat Design and Construction   4 Weeks Ago
Replies: 811
Views: 31,920
Posted By MikeJohns
Re: Steel vs Fiberglass

Brent I'd better address this or from experience it will be used again and again.....



You were told that a point load ( mast support) that was taken to the hull plate was bad practice. It...
Forum: Sailboat Design and Construction   4 Weeks Ago
Replies: 811
Views: 31,920
Posted By MikeJohns
Re: Steel vs Fiberglass

You are lucky in the US having some cheap reliable fabricators of CF that can prosper with a high enough demand. In many areas of the world it's very expensive or has to be imported from the US which...
Forum: Sailboat Design and Construction   4 Weeks Ago
Replies: 811
Views: 31,920
Posted By MikeJohns
Re: Steel vs Fiberglass

Brent made that up as usual I have never said anything of the sort. He makes a game out of defaming people he finds a threat.
Forum: Sailboat Design and Construction   4 Weeks Ago
Replies: 811
Views: 31,920
Posted By MikeJohns
Re: Steel vs Fiberglass

Nothing fancy just Robust as the adjective is defined. Robust design from a structural viewpoint, forgiving of operator error and manufacturing defects and maintaining a good level of reserve...
Forum: Sailboat Design and Construction   4 Weeks Ago
Replies: 811
Views: 31,920
Posted By MikeJohns
Re: Steel vs Fiberglass

From a simple structural view it's more robust, that's all. It's a beam with three supports rather than a cantiliver. Sure it depends on the craft and it's construction and the flexural rigidity of...
Forum: Sailboat Design and Construction   4 Weeks Ago
Replies: 811
Views: 31,920
Posted By MikeJohns
Re: Steel vs Fiberglass

If the partial skeg is kept under 30% of the chord length (chordwise) the form has quite reasonable lift drag characteristics and the benefit of balance.

It's a lot more robust than the full...
Forum: Sailboat Design and Construction   4 Weeks Ago
Replies: 811
Views: 31,920
Posted By MikeJohns
Re: Steel vs Fiberglass

Bob

The flow is tripped partly by the angle starting to become acute enough and partly by the flow from the high to the low pressure side through the gap causing early separation itself. That...
Forum: Sailboat Design and Construction   06-26-2015
Replies: 811
Views: 31,920
Posted By MikeJohns
Re: Steel vs Fiberglass

That just the effect of the gap between the skegs trailing edge and the rudders LE, using a sealing strip smooths that perturbation out.

Just to make it clear that the plot I posted was tank test...
Forum: Sailboat Design and Construction   06-25-2015
Replies: 811
Views: 31,920
Posted By MikeJohns
Re: Steel vs Fiberglass

There is a very clear guidelines on immersed steel coatings. It sounds like your paint rep is a bit confused. There is a clear consensus that zinc rich paints only belong in atmospheric not immersed...
Forum: Sailboat Design and Construction   06-25-2015
Replies: 811
Views: 31,920
Posted By MikeJohns
Re: Steel vs Fiberglass

Am I reading this correctly; that you have a zinc based primer below the waterline ? If that's the case then that's your main problem. Zinc based primers shouldn't be used immersed, they will simply...
Forum: Sailboat Design and Construction   06-25-2015
Replies: 811
Views: 31,920
Posted By MikeJohns
Re: Steel vs Fiberglass

Everything in boat design is a compromise. The ideal rudder post is vertical, what Bob has drawn is not at an extreme angle and the advantages are an increased aspect ratio from the root gap...
Forum: Sailboat Design and Construction   06-25-2015
Replies: 811
Views: 31,920
Posted By MikeJohns
Re: Steel vs Fiberglass

Unfortunately Copper-Nickel displacement boat hulls actually foul quickly without anti-fouling, Unpainted it also corrodes slowly in seawater.
Any bare metal hull can become a sacrificial metal...
Showing results 1 to 25 of 106

 
 
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