Not happy with the stem of this boat

While I have used Rhino for years to design boats, I’ve attempted a method that for me is new as to the design feature of the stem of this displacement power boat hull. In essence, I’ve blende both the upper works of the port and starboard sides as well as the lower hull portion of both. In theory this should work just fine. But, if one examines the entire polysurface using “analyze surface” , the results are not satisfactory. I also checked for curvature fairness by running numerous horizontal sections through the stem area and when examining the resultant waterline curves, there exist a break in continuity. Any help would be greatly appreciated

@Robb I assume you can’t upload the .3dm file for proprietary reasons, I have some ideas but need more information.

Can you post a picture with isocurves visible, and a picture with the control points visible?

What degree are the surfaces?

How have you “blended” the surfaces?


Hi Robb, I am looking at your hull to learn something. Do you have a radius going the full length of the keel as well as the stem? May I ask what your normal method is?
For me this is a tedious area to work on getting right. I’ve got your post bookmarked. Thanks for sharing,Mark

Haven’t got too the keel area yet, but it’ll look something like this thirty footer (see attached)…thanks for the contact.

I more or less finished the outside geometry of the 45 footer that is also attached. I’m going to address a rather full length keel for lateral stability after we determine whether we use motor pods or straight shafts for the props. The choice will impact the aft end of the keel. I’ve gravitated towards two 30 KW, twin chamber, water cooled electric motors that run on 48 VDC. This combination looks awfully efficient on paper and will propel this boat to just about 10 knots top with an 8-8.5 knot cruise capability according to Holtrop calcs. She will also carry a 20 KW gen set located under the aft cockpit. It appears that for now, battery tech simply hasn’t arrived to a level to sustain a boat like this for more than a couple of hours at best with a large bank of lithium-ion Tesla type batteries.

It also appears that I may have found a production builder that is excited about tooling this boat up for production. Needless to say, that would make my day!

Cheers, Rob

Hi Robb, as you can see I scribbled over your hull. On the left side , these are deliberate discontinuities I am guessing. As you said only in the stem area.
Is it that it is trying to come together at the lower end of the stem to a single point? Or maybe I am seeing wrong. I guess you have already been down the pipe and slice road then blending. —Mark

Yes there is deliberate discontinuity at the join of the primary and upper sheer. It was my hope to bring it all to a state of continuity at the stem. Now, all that said, if one looks at the finished boat as it appears in the series of renderings, the discontinuity of the two sheers makes sense as the upper sheer is broken albeit smoothly to make a more pronounced bow as one would likely see in a real fishing trawler. So it is that the stem area that appears to bulge slightly is of concern to me. I did, however run a number of waterlines through that specific area and checked the curvature graphs which were not half bad.

There’s no question about it, it’s a tricky area and one that’s quite difficult to make perfect. The shop floor could easily fair that up if any real life unfairness showed up, but I’ve been using Rhino since it was a pre-release download for boat design and have created countless boats with. None, though that have this particular combination of features that creates this particular conundrum.

Thanks for the email, and take a look at the attached; it doesn’t appear to bad. Cheers, Rob

I’ve attached the Rhino file and a couple of rendering of the near finished exterior. I should mention that any discontinuity between the main hull sheer and the upper works sheer is moderately acceptable as it is meant to be viewed as two separate entities that when combined make for a sensible trawler like appearance. It’s specifically attempting to get the stem area where things sort of all come together to be of a continuous nature. All that said, it looks moderately eye sweet as is as seen in the renderings but I’m seeking something a bit more perfect in that specific area of the bow. I’m almost entirely a sailboat designer and have been for quite a while and this is my first foray into this sort of bow. The stem pieces were formed as surface blends with tangency as the primary consideration. Many thanks for your email, Rob

September 27 hull with greater Z value.3dm (3 MB)

Why the 4 rows of control points close to each other at the top and 4 columns of control points at front of the lower side?

Here is my attempt at that
hull.3dm (1.7 MB)

Thanks for the work you’ve done on the stem. May I ask what sort of surfaces those are and how you arrived at that? I had tried network srf, blend srf, loft, patch, etc. I did notice that you introduced a curve on the lower section of the stem at the centerline. That might be it in terms of providing an appropriate amount of control to arrive at a more contiguous stem. Nicely done. I am humbled indeed! Many thanks, Rob

i tried with ExtractIsocurve then BlendCrv both indicated curves with G3 then Sweep2.

hülle.3dm (3.0 MB)

You made those surfaces. I just moved a few of the control points. But first I did a RemoveMultiKnot on the surfaces. That is an important step if you want something that looks good
You can compare the control point locations to your original
I used scale3D and scale 2d to move points so that the symmetry and tangent continuity were maintained.

That curve is just a reference line. I used scale 2d to move a couple points on the upper surfaces. snapping to the centerline to move a pair of points symmetrically. After moving those points I used matchsrf to restore the middle blend back to tangent,

1 Like

Most excellent Obit Wan. I did not think to extract the isocurves as I usually work in ghosted display mode with iso’s turned off as things simply get a bit too complex looking when all the details are in place. I shall be using this method in the future. Many thanks, indeed, Rob

Well you’ve taken a veteran Rhino user who was simply too lazy or too involved in his own work to learn (read: both reasons!) something new to me and very useful. Can’t thank you enough. Got a feeling I’ll be using this sort of bow more often now…cheers, Rob

preferably of course having iso curves hidden by default which can be extracted at any position of a surface. ghosted is a pretty display mode and a bit slow on my computer but if you have the juice for the omni visuality then obit shall be when it has to.

I7 3930 K overclocked to 4.25 GHZ on water with plenty of ram. Four year old system and went with a hexacore ‘cause at the time it was the most affordable high core count for rendering in Flamingo. Two Samsung ssd’s in raid 0 back up every four days to one of two mechanical drives. It’s been totally reliable but I’m ready for a newer system as soon as I can afford it. Thanks for your help with all of this, I’m quite pleased with the shape of things now. All the best, Rob

It may be a bit off-topic, but how do you render your water? It looks really great. Until now i mainly used Rhino for construction, so my knowledge of rendering is a bit limited.

I render in Flamingo; use their water material from the “marine” library as a ground plane, and often tweak the setting in the material a bit depending upon the effect I’m trying to create. I sometimes make the waves large, tweak the repeat pattern a bit or in the case of the attached that is rendered in foggy conditions wherein the sea state is so often calm, I reduce the wave height and pattern a bit to reflect the reality of the scene. I probably tend to overdo it a bit creating something surreal as opposed to real! Thanks for asking, Robb

can you actually cross the atlantic with this one? whats it propulsion? was wondering for a while what the smallest possible but still secure size of a boat would be which could do that.

When I was 15 I wax crew on a thirty foot steel hull, Dutch built cutter that we sailed from New Jersey to Bermuda. We inadvertently sailed through the southeast quadrant of a hurricane that had been forecasted much further north than it was in reality. We sailed under bare poles and suffered some damage but made the voyage in six days in spite of the weather. So, the answer to your question is, it’s a forty five ft., two sleeping cabin boat designed by a retiring sailor for retiring sailors! It could possibly cross an ocean as we did part of the Atlantic in that little thirty footer. The hull is designed to be stable yet slippery enough to run on two 30 KW electric motors with a 20 KW gen set located aft under the aft cockpit and away from most of the occupied portions of the boat.
It is most definitely a displacement hull form and Holtrop calcs show that with the described motors, it will top out at just about 10 knots and cruise quite well at 8.5 knots which gives it a comfortable 100 mile range in protected waters such as the Intracoastal Watery. It would be ideal for coastal cruising up and down the east and west coast, the Islands, and Mexico to say noting of the Med. I want one myself!

Thanks again, Robb

1 Like