Bulbous Bow Canoe

That's why it is very important to have an SOR before any drawing work is done. Far too many, especially amateurs or those wish to build their own boat (like Saqa), only focus on what they can do, that being getting some freeware and drawing a "boat" looking shape. With no appreciation of what effects that shape (as you have described) has on the performance and is never linked to their SOR.

We have designed cats like the one described, BUT, it is to fit an SOR and part of that is understand the limitations, design wise, of that hull in the hydrostatics and the resistance. The hull is thus to fit the SOR envelope of what is or is not possible with said hull form.

I see where you're going now.

For the BB idea ignore that, just simply extend the hull fwd. Take a line some 500m or more fwd of the existing stem and then create a faired surface back into the hull. BUT..before you do this, i would recommend you get someone to draw this up the before and after, to establish from the hydrostatics whether the shape drawn, and/or the size, is enough to correct your trim problems.

 

I agree re design, the boat was designed by Crowther and I am sure with the exact loading he designed for all would have been great, and the design very fast. Reality of live aboard cruising then gets in the way. However the boat as it is now, is still a very fast cruiser able to average 200mile a day the very first time I actually took it on passage and can average speeds over 10K for over an hour easily with flat water speeds of sustainable 14K in only moderate conditions. So not all is lost

I included my BB solution on this thread as it was relevant. My other solution was a full bow extension as you mentioned. The end result will likely be more favorable, but the cost weight and effort likely much higher.

I did plan on doing the design and calculations myself, which I would have posted somewhere on the forum to be scrutinized.

 

The boat seems to work reasonably well, so be careful before mods. Personally I would leave it as it if the boat is safe. I'm not kidding but a good paint job can make visual miracles...
Ad Hoc is right a bulb is not a good solution. Bulbs work in a very narrow range, on merchant ships is not a problem as they spend most of the time at the same speed so optimization is done for the planned speed.
I'll add that bulbs in your case won't give enough volume. Anecdote; I saw the bulbs' fashion 35 years ago; a complete failure. Sailboats have a very wide range of speeds and have to much movements of rolling and pitching.
Your problem of bow down is a problem of "misplaced" center of gravity. It's not the first Crowther exhibiting this problem, I remember 2 Catanas made in France in the Cote d'Azur. As often the true cruising displacements were underestimated...
On race trimarans the solution is brutal; the boat is cut around the middle and center sections are added. The repartition of volumes are thus redefined and centered. If the length of tri can't be changed as on the ORMA 60 feet the tri goes to heavy mods or more probably is trashed.
Another possibility is to move the weights in the boat; ie the tanks. Difficult on a cruise boat. Total sacrilege and desperate: rear ballasts, but that solution has its cortège of nuisances.
The old Skerry Cruisers had often the same problem; the solution was to make a longer bow screwed over the original bow. That worked pretty well.
Such a solution will work on your boat but it's pretty expensive as you have to redraw all the front part of the hulls, make molds, and install the extensions. I'm not sure that all this job and expense are worth...

 

Thanks for the reply. The best solution is undoubtedly (ignoring cost, time and skills needed) to extend the bow, which will also make for a more favorable DLR.

The bulb was a second choice option, based not on purely the best outcome, but on the outcome VS cost, time and skills needed. With an understanding of the limitations, of extra drag when sailing out of its speed range and design, no extra waterplane area forward so the bow will still be just as sensitive to loading etc. Which are all inferior to an actual hull extension as noted. The SOR of this bulb modification is simply to correct trim, not to give a performance increase. I would be happy with trim correction and a small but almost negligible performance decrease. Increased average speed may still be likely due to not having to slow the boat due to reduced slamming when sailed offshore.

A friend of mine owns the famous 40' Crowther racing tri "bullfrog AKA verbatim". The original owner fashioned various streamlined style (sharp leading edge and keel) bulbs, of ever increasing size to this boat. Finally he was happy with the result after 3 attempts (this boat still holds some race records I believe). It looks fair and well done, in a boat yard with about 10 different bulbs I would not want to have anywhere near my boat. The whole job took him 3 days to make the bulb. So it could be thought of as disposable if its a failure. Whats more I have a mold of this bulb from this boat!

That all said, I am still reluctant to try it given its many limitations. I have not yet determined the added buoyancy, and as you say it may not be enough anyway.

There is no way I will be adding any weight for the only purpose of sinking the sterns so that the bows will raise slightly. Weight is the enemy. Well its more of an enemy at the bow than the stern in this case, but its still an enemy in any area on my boat

As mentioned all movable weights are moved aft as far as possible. The tanks are empty most of the time, so I do not see a great benefit from moving them. Though it certainly would help a lot when they are full. But the cost and effort would be fairly large also. I think that that cost and effort would be better put toward a bow extension.

I have been trying to read up on bow extensions, and there was not much I could find. But I know its a fairly difficult job as the hull needs to be faired back a long way, otherwise you just end up with a low Cp nose that has little buoyancy.

I think I will start a separate thread on bow extensions with the hope of finding some examples which I can study to determine if the build is within my current or acquirable skill set.

 

You have to calculate how much volume is needed to get a boat on "normal" and aesthetic lines, you'll be surprised... That's the start. After you have to see the effect of the added volume on the prismatic coefficient (generally good) and of the move forward of the center of displacement (maybe not good). After you have to estimate the effects of the added lateral area; tacking will be maybe more difficult. And to estimate the effects of the added bow on the lateral center of resistance ie the trim of the boat; weather helm or the contrary. Maybe bigger rudders will be needed.
It's the work of a (good) naval architect with expertise of catamarans.

The difficulty of adding a bow by itself is not great, it's just a question of lofting but the realization can be expensive. If the boat has not problems of security when sailing in rough conditions, apart a bow down attitude but without engaging in the sea, it's would be wise to abstain about modifications.
Another possibility is to add freeboard and reserve volume at the bow, it's maybe a simpler task.