Mono Transom Extension, Anyone?

[colemj]

Don't compare with catamaran extensions. Catamaran hulls are very easy to extend because the hull form is mostly narrow and uniform and extensions rarely change the prismatic coefficient and catamarans do not heel to any extent that changes the hull shape in the water on different points of sail. You can almost pull the hulls out as long as you like with little change in characteristics.

The examples of mono extensions above are primarily of extensions that exist above the waterline.

If you intend to change the hull below the waterline, you should have more design and engineering information on your particular boat before proceeding. Changing a mono below the waterline has the potential to change almost every carefully designed quality of the boat.

However, it sounds like you are intent on this, so go ahead! We are all waiting for pics and experiences.

Mark

[Sailmonkey]

I crewed on the 72' Bristol "RAJ" that had a stern extension done to lengthen the boat to 83'. The extension caused the boat to steer horribly, the AP was always running shifting the rudder side to side to maintain a course.
It can be done well or poorly, some boats will be more tolerant of this treatment than others.

[daddle]

Do it. The ones I've seen were nice. In the 2 to 3 foot range. Only underwater at high speed. All help the water flow when the stern drags at speed. If you are clever it can bolt on with one tidy seam line.

They are often built using the boat as a molding jig. A piece of thin ply bent around the existing hull, extending aft, is a good start on a fair shape.

Great swim step. However the typical cruiser will probably use it as a garden area or Jerry jug storage, ugh!

[SURV69]

Forget the swim platform.

I'd like to add a raised 2'(or so), poop-deck to my Newport 28, so my cats can sit and watch me work.

[boatsail]

Found this online

Sovereignty Projects - Sovereignty: A Unique Catalina 27 (hull # 65)

[Bash]

check out this thread for a good look at a professional scoop job: http://www.cruisersforum.com/forums/...ver-74299.html

[gts1544]

RabidRabbit, Go to the CLASSIFIED section and look up SHARED CORPORATE OWNER MEMBERSHIP. REGGAE is a Beneteau Idylle 11.5M flat transom (originally) until the original owner added a 3.5' sugar scoop swim platform which we love. We can't imagine not having this modification, though I can't speak to any speed increase as we have never been without it.

[thinwater]

Speed/hull speed. Unless the transom is loaded far beyond design this is generally minimal. Sure, you can eliminate some burbles, but unless the lines are quite long, you can actually increase drag. Increased waterline? Moving from 34' to 36' could gain you 0.23 knots... but you have also added weight but no power. Unless you up-rig at the same time I would not expect to find it.

Speed/multihull. Not so clear. Generally somewhere around 10 knots the wake begins to separate from the transom cleanly; unless you modify the entry too, top end speed doesn't change. Weight and wetted surface rise.

Ride. Cats, which can hobby horse in certain conditions, can often greatly benefit from transom mods, particularly for a specific sailing area. This is the real reason for cats. Would this apply to a mono? Perhaps, but certainly less so.

Storage. Sure, you will gain load carrying capacity. Could make sense for certain designs, not for others. And I love my sugar scoops.

Space. Length does not add useable space, as the beam is fixed and the extension will be sealed.

------

Doing a good job--one that will not lower the resale value of the boat--is quite an undertaking. Is it worthwhile? The answer depends on the design, the goals, and the owner. I would focus my design on ride and access, if it were me. The only boats I have personal expereince with are Stiletto cats; the stretched cats are smoother but not faster unless other mod are made. Often as not, the whole rig is changed as part of a refit, so comparing most of the modified boats to stock is apples to oranges.

[RabidRabbit]

So I did mention sugar scoops, because thats what most extension mods are for. I however have no interest in a scoop at all. My transom is huge (7x4) roughly and my thoughts were to extend the lines back 30" and then put a similar but smaller transom on. This area would have a deck access hatch, house a watermaker and be storage for things I never seem to use. Then my current swim platform would go back on. the swim platform is at deck level allmost, when stepping from boat to platform the difference is only 3". This boarding deck has a 2" pole on each side for windgen and future radar, and davits that can lift 600lbs.

[Bash]

Originally Posted by RabidRabbit

So I did mention sugar scoops, because thats what most extension mods are for. I however have no interest in a scoop at all. My transom is huge (7x4) roughly and my thoughts were to extend the lines back 30" and then put a similar but smaller transom on. This area would have a deck access hatch, house a watermaker and be storage for things I never seem to use. Then my current swim platform would go back on. the swim platform is at deck level allmost, when stepping from boat to platform the difference is only 3". This boarding deck has a 2" pole on each side for windgen and future radar, and davits that can lift 600lbs.

On a center-cockpit ketch?

Too radical.

At what point does it become a forward-cockpit ketch?

[RabidRabbit]

Whats too radical? 30" of transom, mostly all above the water line.