Bulb design/positioning

The boats that sail better have more conservative keels. They are wider, so they don't need to widen, and at the same time, they have smaller bulbs both in weight and weight distribution. With equal weight, they would be chunkier and shorter. I believe this favors that if the water doesn't enter at the correct angle, it's not as serious.

I've been adjusting so many details on the boat that now I believe this is the one I'm missing. Originally, I moved the mast backward because the boat wasn't pointing well. Once I adjusted that, I noticed that the boat pointed better but leeway increased compared to the others. So, I increased the lateral surface area of the keel, and that improved a lot. Then, I changed the rudder to a sleeker one, and that also improved performance at all angles. Now, I think the only thing left to adjust is this bulb issue.

 

I really doubt that altering the angle of the bulb will make any noticeable difference to the windward performance.You are presumably familiar with the equation for calculating the lift generated by the keel and the items you need to keep in mind are the Cd and the A since the density of the water is not something you can control.Can you advise us of the section chosen,so that we may take a look at the lift characteristics and what area do you have?

The easy fix for the protruding edge of the fin at the hull junction is to add a sensible blend fillet to the forward end with microballoons or similar and maybe something similar at the trailing edge.It will be a much easier project than adjusting the bulb-unless you have run a CFD simulation on the revisions you intend and have a positive result to justify all the effort.

 

Unfortunately, I am not a naval engineer. When I finished school, I wanted to study naval engineering, but the naval engineers I contacted discouraged me because there were not many job opportunities in the country, as the sailing market is small. However, I have always liked it a lot and try to get involved as much as possible.
I designed the boat's rudder based on Jefa rudders' plans and with the help of someone who works in wind energy and was familiar with these simulations.
Here, I consulted abaut the bulb and they couldn't tell me the effect.
Reading the responses, I realize that I didn't explain all the information. My boat has much more sail area than the others at the stern (85 vs 70 or less m²), so it's to be expected to be faster downwind. We race with a fixed rating, so when the wind is from the stern, it favors me, but I've noticed that many times we don't gain as much advantage over the others as we should.
Although we go faster, the difference is not as much as the ORC software predicts. I also believe that if the boat pitches 2 degrees when sailing downwind (I am looking into how to measure it better, but it seems to be close to that), aligning the bulb with this should improve performance both upwind and downwind. What I can't estimate is the effect of those 3.5 degrees of difference. I am uploading some diagrams of the bulb profile in case they help.

Last weekend, we won a regatta by 5 minutes on corrected time, despite the fact that for half of the race we used a code zero while the rest used a genoa, and for another part we used an asymmetrical spinnaker while the rest used symmetrical spinnakers but were on the edge and couldn't handle it as well as we did. On the water, we gained a 30-minute lead, but according to the ORC VPP, it should have been more. I am uploading the VPP for both.

 

Have you considered that the larger rig might be the cause of the boat pitching slightly nose down when sailing offwind? I really don't see how the angle of the bulb to the waterline is making as much difference to the speed as other factors and it will be a considerable exercise to do the experiment.Could you post an image of the cross section of the vertical element of the keel?How does the total lateral plane of the boat compare to the other similar boats?Would you think that a keel profile similar to the example attached might be worth considering?

 

ORC_VPP does not calculate the Pitch effect on the hull (and certainly not on the bulb); neither does my VPP because i do not know how to calculate it, although i am obsessed with the bow not sinking and i calculate so that it does not sink.

Upwind ... A powerful rudder can cause the bow to Pitch/sink because the lateral force of the rudder with the sailboat heeled has a vertical component.

Downwind ... It is the force of the sails and their large lever arm that Pitch/sinks the bow of the sailboat.

 

Professor Keuning says that the effect of Pitch on the Downwind Hull can be as high as +20% resistance due to Wave formation (bulb is not mentioned).

 

This is one of the reasons that triggered (2014-) the now seemingly unstoppable Trend of wider or bulky bows on powerful sailing yachts.

 

Professor Keuning proposes the following formula to estimate the effect of Hull trim on Resistance

 

"Wet feet" I have not considered changing the keel. First, I would like to optimize this one for costs, and if there is no other option, I will move to a more conservative but proven one.

I also notice that my boat pitches its bow downwind, but this happens to everyone. In fact, the model of my boat has a bow with more volume than others, so if the effect could be measured perfectly, I suppose it pitches less.

Other boats with the same design as mine have more conservative keels with a larger lateral surface area (30% more area and wider), so their sword weighs 350kg more and the bulb 200kg less, achieving the same righting moment.

Carlos: When sailing upwind, isn't the effect of the sails pushing the mast forward and the keel pushing backward similar to downwind, but when heeled over it's harder to notice?

I think in the meantime I will see if I can improve the hull-to-keel joint. When I did it, I thought that being attached to the hull wouldn't have a big impact, but in this decision, I feel that I had underestimated it.

 

"When sailing upwind, isn't the effect of the sails pushing the mast forward"

Yes

The sail force has

1) a horizontal component, as is logical, and
2) a vertical component due to Heel and if the center of the sails is forward of the center of Buoyancy, as is usually the case.

Upwind ... Pitch force = the sum of 1 + 2 + 3) the vertical component of the lateral force of the rudder.

In addition also, both Upwind and Downwind, 4) as the bow sinks the water can see a curvature of the hull (further forward) creating a Suction (low pressure) which works sinking the bow.

But what I wanted to underline is that downwind the sail force is usually quite large and even huge (for example 10% of the displacement of the sailboat).

 

Left image: bow down may create more bow down by creating low pressure, suction

 

Thank you very much Carlos. I bought an inclinometer to see if I can measure these effects over the weekend!