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Search: Posts Made By: MikeJohns
Forum: Sailboat Design and Construction   1 Day Ago
Replies: 568
Views: 19,439
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   3 Days Ago
Replies: 568
Views: 19,439
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   3 Days Ago
Replies: 568
Views: 19,439
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   3 Days Ago
Replies: 568
Views: 19,439
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 Days Ago
Replies: 568
Views: 19,439
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 Days Ago
Replies: 568
Views: 19,439
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   5 Days Ago
Replies: 568
Views: 19,439
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   5 Days Ago
Replies: 568
Views: 19,439
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   5 Days Ago
Replies: 568
Views: 19,439
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   5 Days Ago
Replies: 568
Views: 19,439
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   5 Days Ago
Replies: 568
Views: 19,439
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   1 Week Ago
Replies: 568
Views: 19,439
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   1 Week Ago
Replies: 568
Views: 19,439
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   1 Week Ago
Replies: 568
Views: 19,439
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   1 Week Ago
Replies: 568
Views: 19,439
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   1 Week Ago
Replies: 568
Views: 19,439
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   1 Week Ago
Replies: 568
Views: 19,439
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   1 Week Ago
Replies: 568
Views: 19,439
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   1 Week Ago
Replies: 568
Views: 19,439
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...
Forum: Moody   1 Week Ago
Replies: 8
Views: 384
Posted By MikeJohns
Re: Thornycroft engine

Thornycroft marinized a few different engines, Lancing Marine in the UK often marinized the same engines and are the best source of parts for most older marine diesels. Contact them and ask, they are...
Forum: Multihull   03-19-2014
Replies: 307
Views: 27,200
Posted By MikeJohns
Re: How do you feel about catamarans?

I'm sorry this is tardy. I'm in the process of retiring and moving and my world is in as much disarray as the inverted cats :-)

I cannot post copyright material unfortunately but I can provide...
Forum: Multihull   03-17-2014
Replies: 307
Views: 27,200
Posted By MikeJohns
Re: How do you feel about catamarans?

That's precisely the type of observation I'm referring to.

Half way down that web page there is a graph that you are presumably based your statement on.

It compares a 35 foot multihull with a...
Forum: Multihull   03-17-2014
Replies: 307
Views: 27,200
Posted By MikeJohns
Re: How do you feel about catamarans?

I'm presuming that if you anchor a 32' cat for storm conditions it's going to be a sheltered anchorage. :)
Forum: Multihull   03-17-2014
Replies: 307
Views: 27,200
Posted By MikeJohns
Re: How do you feel about catamarans?

No distaste. But soon as conditions deteriorate a sailing Cat is only as safe as the on watch skipper and needs a lot of care. It's important to understand why. Extraordinary caution is required for...
Forum: Multihull   03-16-2014
Replies: 307
Views: 27,200
Posted By MikeJohns
Re: How do you feel about catamarans?

I'd still like to know where you got the statistics you posted earlier about sinking and inversion. And how meaningful they really were if you separated out the types of craft specifically of...
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