Aqua Casa 20 Vs. Millie Hill

I'm examining both of the mentioned designs for a weekend get-away for two, on small glacial lakes dotting the boreal forest in northern Ontario Canada. Power will be provided by a 9.9 hp outboard. Examining both designs the AC has a typical displacement hull as opposed to MH having a straight run to the transom. Can I expect any difference in performance? My goal is to achieve hull speed.
AC has a flat floor, MH has a couple steps down in to cabin with reduced cabin height forward. I assume MH is trying to reduce windage, does AC have excessive windage.
I will be constructing the boat outdoors. Speed of construction is of vital importance as this will be an after hours/weekend project. I have adequate shop space to prefab full length sections up to a height of 6'8" and adequate indoor storage to keep them out of the weather until assembly. Does anyone have any knowledge of construction of these designs? My original plan was to construct Lisa B Good with a 4' stretch in the middle (ya I know this would constitute a new design and the verbal tongue lashing this will bring on!) as most of the components could be prefabbed then assembled.

 

For everybody who is not familiar with these craft (like me), here is some background info -
Aqua Casa -
Aqua Casa Houseboat, Aqua Casa Plans, Aqua Casa Houseboat Plans http://www.berkeley-engineering.com/AquaCasaHouseboat.html



The GA shows the rocker in the hull



And Sam Devlin's Millie Hill which does not appear to have any rocker in the hull.

Millie Hill 20 | Devlin Designing Boat Builders https://devlinboat.com/millie-hill-20/




And as Member has mentioned Lisa B Good, here is some info on her -

https://www.duckworksmagazine.com/09/designs/lisabgood/index.htm

 

Thanks Banjansailor
I would have done it, if I knew how

 

I saved the photos and drawings from the websites to my computer, and then attached them to my post using the 'upload a file' in the bottom right corner of the screen.

 

I'm going to sleep on this question and comment in the morning.

But I am wondering, do you have space for gallons of bug repellent in each design?

Northern Ontario,... are you sadistic mate?

 

Black fly season is always fun, now that we can't buy deet any more they just eat you up! When it warms up they die off and the mosquitos take over, then it's winter again. Screens and a good fly swatter will be a must.

 

Awfully good of Bajansailor to post some details.

I do like the idea of the four foot extended version if it doesn't interfere with the design too much.
I guess it really boils down to which design tickles your fancy the most and which is easiest for you to build given your situation.

Don't be too distracted by "hull speed", it is a commonly misguided term that doesn't really apply here as you are limited by 9.9HP.
Being so similar in size, your total weight (or displacement) is going to be your major limiting factor speed wise.
And remember, you're there for the experience, perhaps the slower hull is "better".

You mention windage.
Is wind an issue where you're going at that time of year?

 

When I put similar hulls through Freeship 6kn seems to be the sweet spot

 

I can tell you my 25' x 10' (8 000 pounds at the time) houseboat moved at 5 knots with a fresh 8hp 4-stroke hanging off the back, WOT.
It was slack tide with no wind. (4.9kts southbound and 5.1 kts northbound). Measured by GPS.
18 degree barge bow, 16' flat (with two sleggs with matching angle, then flat all the way to the transom) and a 14 degree barge stern rising up to the waterline.
So ~23.5' length at the waterline. About 6.5-kts calculated "hull-speed". (I hate that term)

 

According to Freeship I'll need just over 2kw to achieve 6kts and about 5.3kw to travel 7kts. I don't believe the remaining 2kw will give me much if any more headway.

 

@member 69256 I would have a LOT more faith in Bluebell's practical sea trial described above, rather than what Freeship is optimistically suggesting to you.

8 hp is approx 6 kw, yet Bluebell's houseboat (with a longer waterline length) only managed 5 knots flat out.

This is consistent with the observation (quoted below) by Sam Devlin about Millie Hill -
"The new boat floated on her lines when she was launched May 4, 2008 (even with all the gear a live-aboard might have) and with a 10 hp Yamaha hi-thrust outboard, she powers at what I would guess is 5 knots top speed."

 

The design that has rocker is more desirable for a relatively heavy boat that will use a 9.9. The rocker bottom will almost surely allow better fuel mileage and more than likely, more speed. The straight, no rocker, bottom may be a few hours easier to build but it will cause a mess of aft disturbance when in motion. In defense of the no rocker bottom, there will be a bit more enclosed space that might be useful. . However, the additional enclosed space at the stern is not an ideal place to store objects of any significant weight.

 

I was able to put all three hulls into freeship and Millie Hill and Lisa B had a cp around .92 whereas the Aqua casa 20 was around .63. Does the Cp have any effect on these hulls in terms of power requirements. The Aqua Casa had considerably lower displacement than the MH and LB does this have much effect on power requirements at such low speeds

 

Yes, in a way.
What do the designs call for power wise?
Likely a range dependant on your SOR.

 

A Prismatic coefficient of around 0.63 is generally a good 'all rounder'.
This article explains it fairly well.
https://www.sailboat-cruising.com/prismatic-coefficient.html

But if you are a glutton for punishment, and want to get totally confused, this lengthy thread on this esteemed Forum also explains it (albeit with much deviation, variation and accusations along the way, in typical forum fashion )
Prismatic Coefficient https://www.boatdesign.net/threads/prismatic-coefficient.28729/