SeaHorse Hulls PRO for Rhino3D

A parametric catamaran hull design plugin for Rhino and *Grasshopper. This tool simplifies the laborious process of hull lofting by allowing the user to input a few basic parameters and outputs a slender, perfectly faired, high performance catamaran hull. To make the process as user friendly as possible, a few parameters are blackboxed, leading to the creation of a specific family of shapes, therefore, this is not an all-do all-possible design tool. The hull output focuses on the underwater body performance, the freeboard can therefore be trimmed and different shape aesthetics manually added. Free trial available here. For licensing information scroll down to the bottom.

Installation

After downloading the package, run the installer (SeaHorse_Hulls_PRO.rhi) by double-clicking the file and follow the on-screen instructions. Restart Rhino and SeaHorse Hulls will be ready to work.

Commands

shHulls - generates slender hulls based on input parameters
shHullsHelp - opens the documentation page in a web browser page

Prerequisites

Recommended document units are millimeters, this is the default unit the software is tested in, other units may work.

Inputs

  • **Pick up values from last parameter set - automatically loads the last parameter set used for generating the previous hull, if any.
  • Waterline length - is the desired waterline length (LWL) of the finished hull, the overall length (LOA)  is a result of the geometry creation process and it will be different than the waterline length, generally greater than LWL.
  • Waterline length/beam ratio - is the desired waterline length to beam on the waterline ratio. Since this is a main performance driver for a multihull, the overall beam is neglected as an input and it is a result of the geometry creation process, the overall hull beam is generally greater than the beam on the waterline.
  • Waterplane max beam approx location - is the desired location of the maximum width of the waterplane (the intersection of the hull with the surface of the water). Due to the geometry creation process this location can vary a bit and the input is not the absolute result, hence "approx". This parameter is used the shift displacement fore and aft, affecting the CoB and CoF. It is generally accepted that a CoF further aft of CoB will reduce pitching motion. The range is from 0.4 to 0.6 as percentage of LWL, during development, it was observed that values outside this range distort the hull too much, although results may still be usable.
  • Waterplane fullness multiplier - this parameter affects displacement (hull volume) and Prismatic Coefficient by increasing or decreasing the displacement/volume distribution at the ends. Higher value - fuller ends. The range is from 0.7 to 1.
  • Draft - maximum hull draft, due to the geometry creation process the finished hull max draft might be a little off by the order of decimals.
  • Max draft approx location - this parameter allows shifting of the max hull draft fore and aft, directly affecting the CoB and CoF, due to the geometry creation process, the finished hull max draft location might be a little off, hence "approx". The range is from 0.4 to 0.6 as percentage of LWL.
  • Rocker fullness multiplier - this parameter affects the Prismatic Coefficient directly, by increasing or decreasing displacement/volume distribution at the ends. A higher value will result in a "fuller" rocker curve while a lower value will create a rocker curve with less curvature near the ends. The range is from 0.7 to 1.3.
  • Rocker aft curvature (Concave/Convex) - convex results in hull shape with a steadily rising rocker aft, while convex results in a hull shape with a negative curvature rocker aft, or rocker "hook". The latter helps reducing the negative pressure sucking the hull down in the after part, supposedly increasing dynamic lift and helping with planning, refer to theory. Note - the concave rocker aft option does not produce a submerged transom and it reduces Prismatic Coefficient, lower the volume distribution in the after part. If a submerged transom is desired, account for lowering the hull into the water after the creation of the hull blank.
  • Rocker inflection point location - available if Concave rocker option selected. This parameter controls the location of the change in curvature from convex to concave along the rocker length, a higher value will shift the rocker "hook" towards the transom, while a lower value away from the transom. The range is from 0.87 to 0.95 as percentage of LWL. During development it was observed that values outside this range distort the hull shape too much, although results may still be usable.
  • Rocker negative curvature multiplier - available if Concave rocker option selected. This parameter increases or decreases the amount of negative curvature in the after part of the hull, increasing or decreasing the rocker "hook" as well as the Prismatic Coefficient. A high value will result in a hull with an almost 0 degree rocker hull exit angle (increased "hook) while a lower value will result in a hull with minimal rocker negative curvature in the after part. The range is from 0 to 1.
  • Bow sink - by design SeaHorse Hulls can create hulls with a certain amount of bow sink (submerged bow), however, the value cannot be 0 (but very close to it). Increasing bow sinkage will result in a hull with a higher Prismatic Coefficient and more volume/buoyancy forward.
  • Reverse bow amount (wavepiercing bow) - this parameter controls the bow/stem profile. A higher value will produce a typical wavepiercing (negative rake bow) hull while 0 will produce a hull with nearly vertical bow profile. The exact bow profile is a result of the geometry creation process. The range is from 0 to 1.
  • Forward volume multiplier - controls the amount of hull volume specifically in the front lower part of the hull. A higher value increases Displacement and Prismatic Coefficient, shifting the CoB forward by a small amount, while a lower value does the opposite. The range is from 0 to 1.
  • Sheer height - this is the height where the freeboard starts to curve inwards, towards the deck, this is not the overall hull height above the water.
  • Sheer camber amount - this parameter affects the curvature of the sheer line, a higher positive value will result in a convexly curved deck side profile, while a low value (negative) will produce a hull with a concavely curved deck side profile. The range is from -0.2 to 0.2.
  • Transom sheer drop multiplier - this parameter controls the rise or fall of the sheer line towards the transom. A high positive value will produce a hull with the sheer line sloping DOWN at the transom (lowered transom) while a low negative value will produce a hull with the sheer line sloping UP at the transom (high transom). The range is from -0.3 to 0.3.
  • Sheer sharpness amidships - controls the roundness/sharpness of the sheer in the sectional profile amidships. A higher value will produce a more rounded sheer, while a lower value will produce a sharper freeboard-deck transition. The range is from 0 to 1.
  • Sheer sharpness at bow - controls the roundness/sharpness of the sheer in the sectional profile near the bow . A higher value will produce a more rounded sheer, while a lower value will produce a sharper freeboard-deck transition. The range is from Sheer sharpness amidships to 1.
  • Sheer sharpness at transom - controls the roundness/sharpness of the sheer in the sectional profile near/at the transom . A higher value will produce a more rounded sheer, while a lower value will produce a sharper freeboard-deck transition. The range is from Sheer sharpness amidships to 1.
  • Deck slope amount - controls the amount of deck slope sideways. A higher value will produce a hull with a centerline deck crease sloping down towards the sheer. this will shed water fast and it is typical for a wavepiercing hull, helping with rapid recovery from a nose dive, while 0 will produce a flat deck cross sectional profile. The range is from 0 to 1.
  • Transom bottom fatness - controls the width of the transom compared to the max hull width. A higher value will produce a hull with higher displacement aft, higher Prismatic Coefficient and supposedly increased dynamic lift while a lower value will produce the opposite. The range is from 0.7 to 1.

Typical output

If all goes well, the shHulls command will produce two typical outputs linked to each other:
  1. A geometry object inside Rhino3D, your hull with a unique geometry ID. The hull is placed with the waterline entry tip in the Origin and lengthwise placed along the OX axis. The hull is generated in the loading condition with the transom always touching the water. For a submerged transom consider moving the hull on the OZ axis and account for bow sink and draft from the early beginning.
  2. A parameter report .txt file saving all the parameters used for the generation of the hull. The .txt file naming (string formatting - YYYYMMDD_HHMMSS_shHulls_ParamReport.txt) will include the system date and hour when the hull was generated. The report itself includes the version of SeaHorse Hulls that generated the hull, the hull unique geometry ID and the parameters themselves. The report file is saved inside the folder where your Rhino .3dm is saved, if you are working on a new unsaved file, the report file will be saved on your user's Desktop. This report file is linked to the hull geometry inside your Rhino .3dm file by a hyperlink and it can be instantly opened by clicking the URL from the Properties Pane in the "Hyperlink" field. This allows easy identification of hull generation history. However, if the files are manually moved, the file cannot be opened by a single click in the "Hyperlink" field from Rhino anymore, since the path changed and it will have to be manually identified by the geometry unique ID or object name (starts with same system date/time string as in the .txt file).

Licensing

To be announced.
*unreleased
**being implemented