HM19 10hp cruising speed?

Ask questions before buying our plans or request a new design. Anybody can post here
TomW1
Very Active Poster
Very Active Poster
Posts: 5844
Joined: Sun Apr 19, 2015 10:57 pm
Location: Bryson City, NC

Re: HM19 10hp cruising speed?

Post by TomW1 »

It duplicated on me, sory. Tom
Restored Mirror Dinghy, Bought OD18 built by CL, Westlawn School of Yacht Design courses. LT US Navy 1970-1978

User avatar
OrangeQuest
Very Active Poster
Very Active Poster
Posts: 3944
Joined: Tue Aug 28, 2018 1:14 pm
Location: Houston, Texas

Re: HM19 10hp cruising speed?

Post by OrangeQuest »

Yes, I understand that one hull is designed to be a planning hull and one is not. But does that mean a planning hull at less than planning speed, displacement speed, will not perform as well as a designed for displacement speed hull?

In other words, a 10hp motor will push a planning hull at the same speed as a displacement hull for a give weight if the DWL are the same in both length and width of both hulls? And are the two hull designs at displacement speeds the same DWL for the same weight?
"that it isn't just an ordinary sort of boat. Sometimes it's a Boat, and sometimes it's more of an Accident. It all depends." "Depends on what?" "On whether I'm on the top of it or underneath it."
A. A. Milne

Bogieman
* Bateau Builder *
* Bateau Builder *
Posts: 1992
Joined: Wed Jun 15, 2016 12:20 pm
Location: Myrtle Beach

Re: HM19 10hp cruising speed?

Post by Bogieman »

Man, I really messed up my orignal question :lol:
I should've just asked: What is the expected top displacement speed be for the HM19.

Bogie

TomW1
Very Active Poster
Very Active Poster
Posts: 5844
Joined: Sun Apr 19, 2015 10:57 pm
Location: Bryson City, NC

Re: HM19 10hp cruising speed?

Post by TomW1 »

My calculator shows up to displacement speed range speed of 6-14mph since this is a planing hull. But the displacement speed calculated was 6.07mph for the boat and motor combination. So, if you compare the HM to the HMD there is an added 3" in draft and some other differences in shape between the two designs. It would be hard for the HMD to reach much over 7mph even with a lite load. Your correct in your statement "if everything were equal" but in real life a displacement boat would never be the same to float the same DWL.

Tom
Restored Mirror Dinghy, Bought OD18 built by CL, Westlawn School of Yacht Design courses. LT US Navy 1970-1978

User avatar
Evan_Gatehouse
Very Active Poster
Very Active Poster
Posts: 3210
Joined: Tue Aug 27, 2002 1:00 am
Location: Vancouver, BC, Canada

Re: HM19 10hp cruising speed?

Post by Evan_Gatehouse »

Well both HM and HMD. Both are at displacement speeds here.

Here is a boat test of a Lud Impact 1775, an aluminum open fishing boat. As light as a HM19 I would guess. Moderate V hull

http://www.boatmaginternational.com/636 ... roke-f115/

Notice the fuel consumption at 5.2 knots. 1.1 gph is about 10 HP in a 4 stroke gasoline engine.

Image

To get it to 7.4 knots you nearly double the fuel consumption so you're around 18 HP.
designer: FB11/GV10,11,13/ HMD18/
SK17,MM21/MT24

OneWayTraffic
* Bateau Builder *
* Bateau Builder *
Posts: 1662
Joined: Sat Jan 10, 2015 7:13 pm
Location: New Zealand

Re: HM19 10hp cruising speed?

Post by OneWayTraffic »

OrangeQuest wrote: Sat Feb 11, 2023 12:39 am Yes, I understand that one hull is designed to be a planning hull and one is not. But does that mean a planning hull at less than planning speed, displacement speed, will not perform as well as a designed for displacement speed hull?

In other words, a 10hp motor will push a planning hull at the same speed as a displacement hull for a give weight if the DWL are the same in both length and width of both hulls? And are the two hull designs at displacement speeds the same DWL for the same weight?

Obviously, at displacement speeds the hull designed for such will be better. It will be more efficient, track better, ride more smoothly. It will not be faster unless you are operating with very limited hp. 10hp is 10hp, but the displacement hull might go the same speed with 6hp.

User avatar
Evan_Gatehouse
Very Active Poster
Very Active Poster
Posts: 3210
Joined: Tue Aug 27, 2002 1:00 am
Location: Vancouver, BC, Canada

Re: HM19 10hp cruising speed?

Post by Evan_Gatehouse »

If you want to always go slow pick the HMD. If you think you might plane one day and go fast, pick the HM. You can still go slow with the HM with a small motor.
designer: FB11/GV10,11,13/ HMD18/
SK17,MM21/MT24

TomW1
Very Active Poster
Very Active Poster
Posts: 5844
Joined: Sun Apr 19, 2015 10:57 pm
Location: Bryson City, NC

Re: HM19 10hp cruising speed?

Post by TomW1 »

Bogieman just put your 10HP on it now. When you are able to upgrade to a larger motor do it. I will be glad to work out what your speeds will be depending on the HP you choose. Right now, Evan and I are sort of in agreement but with some terminology mixing us up. Just remember you have a planing hull which will be more efficient once you get into planing speeds, at displacement speeds the boat is not efficient though the 10HP motor may be. I would try to save up and get the 30-50 HP as soon as possible.

Tom
Restored Mirror Dinghy, Bought OD18 built by CL, Westlawn School of Yacht Design courses. LT US Navy 1970-1978

Bogieman
* Bateau Builder *
* Bateau Builder *
Posts: 1992
Joined: Wed Jun 15, 2016 12:20 pm
Location: Myrtle Beach

Re: HM19 10hp cruising speed?

Post by Bogieman »

Thanks all!

Post Reply

Who is online

Users browsing this forum: No registered users and 4 guests