Bow modifications, who has actually done it?

[KJThomas]

Originally Posted by malbert73

I would avoid adding bulbs. As said earlier they are designed to modify the bow wave but I have read in many places they really don’t work in small boats which frequently encounter conditions with pitching, unlike th large ships who benefit from them.
Unless you were always sailing on flat water lakes, I think they will create more drag and possibly slamming noise.

Bulbs really only work at one speed. Works for ships that have a constant loaded speed. Only reason for adding to a yacht is if you need more bouyancy forward. Adding to the transom and shifting weight aft will do the same.

[thinwater]

Originally Posted by Franziska

Hey, keep it coming. Great resources so far.

@All
Now that we have some boats, I'll try to get in touch with their owners to hear how happy they are with their resulting modifications.

We are planning about a half year refit. So time should not be an issue.
Still, it might be a stepped approach, so we might modify the bows, test the result and do the sterns after a sea trial if needed.

The tricky part will be adding considerably more volume without gaining a lot of weight. Still the way to go will be pretty standart.
Glue on some stations/frames, close the space between with foam strips, sand the lot, glass over and fill with low density closed cell foam.
Filling the voids with XPS foam before glassing is an option but its not preferred as it might soak water over time if there is some water getting in ever.

Attached some pictures of our underwater.
Our primary aim is to make for a more comfortable ride and adding some underwater volume.
If we gain a knot of speed its nice, but not the primary goal.


@VBsail
Could you perhaps forward me a PM with an email of Mollemoks owners? I tried the contact form of CTC but got an error message.
Thanks.

@Thinwater
You are right with the creation of drag when pitching, we will try to fair the bulb in as much as possible though and try not to make it extend forward of the new forward perpendicular. We do not want to snag lines.

@svquintana
Thats about what we consider in combination with a stem modification.

@catsketcher
I agree, modificating the stern will be harder. Especially as we would like to keep the transom hung rudders.

How does she point? So long as you are doing all that, I would research anti-vortex panels or some other keel option. Read the link below! I would look at the rudders too.



http://www.ikarus342000.com/Antivortexp.pdf

[Franziska]

@KJ
You are right about bulbs if one wants to achieve the same goal as on big ships (=reducing wave making resistance and higher speed) in our case (see post 1) that's not the reason we are thinking about it.

@thinwater
Interesting, I'll have a look at it. We have one center board, when it's down pointing ability is OKish for a cruising boat.

Btw. Richard Woods has drawn some very nice hullshape later in his career. The Mira was ne of his earlier Designs. Even than there was a round Bilge version a little later.

[Franziska]

@thinwater
Do you know of anyone who has fitted the anti vortex panels to a hull?

In our case it would be interesting to add them to our somewhat small rudders. But only if we get rid of the Hobie horsing first.

[Dave_S]

Dumb question number .....aaaarh, lost count.

I don't get reversed bows, I get extending the bow but a reversed bow I would think would only offer a benefit in mild seas. If your buoyancy ratio increases at a reduced rate as the bow submerges then in the extreme you must run greater risk of going arse over in bigger seas or more easily done, submerging the bow and stopping or slowing.

Happy to be wrong, have I missed something?

[Dulcesuenos]

Here is a Prout that had bow extensions, it's been for sale for at least 10 years,, interesting bow pulpit. https://tampa.craigslist.org/pnl/boa...686002476.html

Also have a friend doing 3 ft bow extensions on his Athena, he's almost done, not sure it's for me.

[Snowpetrel]

Originally Posted by Franziska

@thinwater
Do you know of anyone who has fitted the anti vortex panels to a hull?

In our case it would be interesting to add them to our somewhat small rudders. But only if we get rid of the Hobie horsing first.

I fitted an end plate to the bottom of my 34 foot mono's rudder. It vastly improved her steering, and in theory should have damped the pitching slightly. Seems like it is a very easy modification that is reversible if it doesn't work out.

[Chotu]

Have done bow extensions. The most difficult part is fairing it into the existing lines.

[Chotu]

This is correct, but the part you are nervous about isn't.

As you press the reverse bow into the water, maximum initial buoyancy is instantaneous, then tapers off a little. This serves to damp the boat's motion in chop.

As you press that reverse bows much farther in, like it would be as you pitch pole, the hull's cross section geometry comes into play. The hull is very narrow at the waterline and very wide at deck level. You still have the same ultimate buoyancy as you press that hull into the water because the hull is wide at the top.

Reverse bows aren't a factor in pitch pole. They are only a factor in reducing poor stability in chop.

The bows and the cross section of the hull itself are both achieving different goals.

[clockwork orange]

Originally Posted by Dulcesuenos

Here is a Prout that had bow extensions, it's been for sale for at least 10 years,, interesting bow pulpit. https://tampa.craigslist.org/pnl/boa...686002476.html

Also have a friend doing 3 ft bow extensions on his Athena, he's almost done, not sure it's for me.

Wow, i'm surprised that Prout hasn't sold at the listed price of $1

[clockwork orange]

Originally Posted by VBsail

Its been done a few times to iroquois both bow and stern. The facebook owners forum has pictures and files library documenting it.

Before


After



During

That is a very nice set of modifications, huge improvement in looks and I would expect some worthwhile performance increase as well. Nice.

[malbert73]

Some boats are worth less than nothing once you factor what needs to be done.[emoji3]

[catsketcher]

Originally Posted by Dave_S

Dumb question number .....aaaarh, lost count.

I don't get reversed bows, I get extending the bow but a reversed bow I would think would only offer a benefit in mild seas. If your buoyancy ratio increases at a reduced rate as the bow submerges then in the extreme you must run greater risk of going arse over in bigger seas or more easily done, submerging the bow and stopping or slowing.

Happy to be wrong, have I missed something?

Yeah - I sort of get what you are saying here. Reverse bows work well when you have no nets, forebeams, bow cleats etc. That is because you get the buoyancy up front without much drag when the bow goes under. In the AC 45s (the non foiling ones) they could dig a bow in and sail fast because the deck did not produce much downward vector - it was slicing through the water like no flat deck ever could. BUT a cruising cat with lots of stuff up front is a totally different story. So you can't just graft a reverse bow onto a boat that isn't designed to push the bow in all the time.

Back to the thread - I have a friend who did a few extensions on his Fastback 30 - it is now 36ft long - all at the back.

What I found interesting was that it was not all positive - in that light wind performance was reduced. This makes sense as the wetted surface is increased and wetted surface resistance is a major factor in drag in light winds. So the OP should not be looking for speed increases in light winds (unless the transom is dragging which is never good in light winds) but for better pitch damping and weight carrying capability.

That said, no one I have ever asked regretted their extensions. Still extending this design is going to be a tricky proposition.

[owly]

Originally Posted by thinwater

How does she point? So long as you are doing all that, I would research anti-vortex panels or some other keel option. Read the link below! I would look at the rudders too.



http://www.ikarus342000.com/Antivortexp.pdf

Just a bit of an update on the AV panels. Bernd has abandoned them for the KD 860 catamaran. They simple do not work...... as per owner experience. Pete Hill, the famous voyager, who currently owns a stretched version of the KD860 that he built knocked off an AV panel unknowingly, and found that it had made no difference whatsoever. He installed low aspect ratio keels. Bernd now shows a centerboard on the KD860.
The theory sounds too good to be true..... and it is. It's necessary to reach below the surface layer of water into deeper water to reduce leeway effectively. This is demonstrated by Richard Woods boats that use either LAR keels or daggerboards. The ones with daggers point higher and make less leeway.


H.W.

[sail4evr]

Excuse my ignorance, how do you send a PM?