Bow modifications, who has actually done it?

[Franziska]

Hi,

there are a lot of older cats around with low CP values.
Many tend to Hobie ([emoji4]) horse to some degree when sailing upwind.
More modern designs avoid this by having more volume designed in the underwater endings of their hulls.
Some of them even get almost bulbous, like the Catana or some Crowther boats for example.

This is less a thread on the pros and cons of modifying but more geared towards the experience of those who have actually modified their bows and or sterns.
How have you done it? How do you like (or dislike?) the results.

The case in question case is not tailored towards a bulb like the ones on big ships, which are typically designed to reduce the wave making resistance by reducing the bow wave.
I'm more after learning about bulbs which add volume and by this reducing pitching.

Few things are of course important.

1)Weight of extension material has to be considerably less than added displaced waters weight

2)Probably one should avoid protrudingthe bulb before the actual stem line as to avoid snagging floating objects & anchorlines.

3)Bulb to be strong enough as to not damage when hitting something. Alternatively treat it as sacrificial.

4)Added shapes to be faired in reasonably well.

So, has anyone done it? Does anyone know someone who has done it?

Thanks for thoughts and ideas, even the ones out of the classic envelope.

[mikedefieslife]

I don't know of anyone specifically that has done it, but some older cats, Prouts and Deans were designed with sacrificial bulbous bows. Whether these helped at all I have no idea.

I alway believe there was a case, maybe even some aftermarket parts to add bulbs to Catalacs. I remember coming across a website somewhere showing the modifications, and maybe even had images on how it was done.

Additionally, I have come across an old Commanche that had some decent stern extensions. The problem with that on older cats though is that many have transom-hung rudders. Unfortunately it's often the stern where they need the most volume too.

Not exactly at the stern but about 80% aft, I have 400kg of engine, batteries, and propulsion, not to mention a dinghy and outboard.

All things said and done, unless you are particularly in love with one of the old style cats, it makes sense to just to get rid of it and buy something more modern. Unfortunately for many of us, there is a huge price jump, that takes some reconciliation. I for example could sink £40,000 into re-fitting and making my Snowgoose as good as can be, and that combined with the actual value of the boat as is, still wouldn't get me a modern production boat like a Mahe 36 or equivalent.

Ultimately though, I would say lack of beam is more of an issue than LWL for the 70s,80 and early 90s era cats.

[Franziska]

Hi Mike,

thanks for the answers. In our case it's the same, we can modify an aweful lot on our existing boat before getting anywhere near the price of a used cat of the newer generation.
As we are able to do also substantial work ourselves the price is even less.

Thats why we are considering this. Optimize what we have, rather run after something we can't have. We rather have money left in the cruising kitty.

If you have any pictures on the modified Comanche stern or the aftermarket mod of the Catalacs I'd surely love to see them.

Thanks,

Fran

[mikedefieslife]

I can't find the info on catalac. Will keep looking.

Here is a little bit of info on a Heavenly Twins cat, that have the bow reshaped to a more modern profile. On a cat like yours or mine, that probably buys an extra two foot of waterline, and a lot more volume/buoyancy.

https://www.sailblogs.com/member/greydove/113103

[Franziska]

Great info! Thanks.

Looks great! Funny enough I did an internship with Pat Patterson (her original designer) in the 90ies.

One thing I am wondering is how the modified underwater profile will affect steering.
In our case we would probably do both ends, but start with the bows.
I'll write an email to Grey Dove to hear from them regarding this.
Guess I need to draw it to see the difference of effort centers.

[Cheechako]

All I can say is my Cat seemed more like zero hobby horsing if you compared it with the monos I've had. Maybe it's a solution in need of a problem?

[GRIT]

As I recall, Rum Doxy has done extensive modifications on the underwater portion of his hulls. If you're wanting to know how to do it, he's the guy who'd know. I don't know if he's on Cruisers forum, but if you google Rum Doxy Catamaran, you'll find his blog. Then, somewhere within, you can read about the myriad of modifications he's done to the boat. They're both real "Can do" people.

https://www.sailblogs.com/member/rumdoxy/gallery/12413/

These are on his blog, which I found on Google, and is publicly accessible, so I assume he'd not have a problem with me publishing the link here.


Cheers.
Paul.

[Franziska]

Hey Cheek, actually newer designs are not doing it much.
Boats which actually have a hullshape akin to a Hobie Cat tend to have this issue more or less pronounced.

Paul, thanks for that. Good info too. Still not sure if they really touched the underwater. The red underwater paint seems hardly touched. Looks like a LOT of work on all above water areas though, and very well done.

Thanks.

[alansmith]

Hi Fran, I am not an engineer. But I spent about half a year in the Napa Marina boatyard and rand across a shipwright who had bought a boat up in the Pacific Northwest. A catamaran....large...beautiful...but had a very low bridge deck. One day i walked over to his boat and asked what he was doing. He said .."she is a slammer and it makes us nutts." So, he was in the process of designing of how to raise the bridge deck by completely redoing the undercarriage of both hulls by extending them downwards by 2 foot.

I looked at all of his mock up scalings and his attempts to get curves correct. I was really impressed with his knowledge and obvious advanced technical skills of trying to basically redesign his boat. After about 2 months he threw in the towel and quit the project. I did notice that him and his wife were no longer talking with one another. Sad thing...i hoped they worked it out.

I'm not saying it can't be done. But what an arduous and technically difficult jog to redesign the point of entry. I think it would be easier to add 5-10 foot to a midsection of a boat then to try and redesign the bow entry.

I know Crowther liked that concept and you can see it on some of his designs. L. Crowther passed away and what a guy he was. I loved his designs. Good luck and let us know what you guys end up deciding on doing.

[multihullsailor6]

Hi again Franziska,

I have done a wave-piercing bow extension ( like the KKG 50 "Victorinox" ) as well as lengthening the sterns to my one-off cat. PM me and I can send you pictures. The boat goes through the waves much smoother now. Longer waterline = speed increase? - can't say.

[Franziska]

Thanks Alan, its a project under consideration. Before heading really into the sunset we plan some larger modifications like reshaping the bowsand partially raising the roof.
Still, we'll keep the old bows intact underneath.

Cutting the complete hull amidship will be close to new building and is to involved. Further that would not make the bow and sterns more prismatic, so the core problem would only get solved by some degree.

At the moment I am hoping to hear about the outcome of such modifications.
Being a boatbuilder initially and having worked in yacht design I do understand the implications of such a modification. Still I need to back the theory up with the experience of some folks who have done it.

Primarily I am looking at underwater modifications, and not so much at things like adding a scoop aft.

Thanks for your thoughts though.

[thinwater]

Transom extensions may be more practical. They really do improve pitching, as well as improving load carrying.

[Franziska]

@Multihullsailor6

PM'ed you. Very interesting. Btw. Speed is nice to have but not our primary reason for considering this.

[GRIT]

I don't see the pictures on the site I linked to. But I'm pretty sure his old blog showed him adding "depth" to the hulls.

I'll look some more.

And here we are:

Before picture: https://www.sailblogs.com/member/rum.../15895/342322/

During: https://www.sailblogs.com/member/rum.../15895/334722/

Bow taking shape:
https://www.sailblogs.com/member/rum.../15895/337768/

Fairing:
https://www.sailblogs.com/member/rum.../15895/337769/
Check out sept 2011 for the underbody mods, and explanation.

My Wife, and Dad, and I are just finishing up our new Catamaran, which we built from scratch. I can assure you, that work on Rum Doxy was a pretty big project, and a clever one too!

These photos should give you a good idea how to go about your project, if you really want to give it a go.

Cheers.
Paul.

[Franziska]

Hey Paul. Now we're talking. Thanks for the searching!