The C-Brats Forum Index
HomeForumsMy TopicsCalendarEvent SignupsMemberlistOur C-DorysThe Brat MapPhotos

Hydrofoil really necessary?
Goto page Previous  1, 2
 
Post new topic   Reply to topic    The C-Brats Forum Index -> Trims Tabs, Hydrofoils
View previous topic :: View next topic  
Author Message
tpbrady



Joined: 08 Feb 2005
Posts: 891
City/Region: Anchorage
State or Province: AK
C-Dory Year: 2005
C-Dory Model: 25 Cruiser
Vessel Name: Bidarka II
Photos: Bidarka
PostPosted: Mon Aug 24, 2009 2:07 am    Post subject: Reply with quote

My engine is as high as it can go without redrilling the top bolt. I can't do that since it is about an 1.5 inches from the top of the transom. With the Permatrim installed any rpm above about 4200 and fuel consumption jumps quickly. Without the Permatrim, I hit steep portion of the fuel consumption curve at 4500 rpm.
_________________
Tom
22 Cruiser Bidarka 2004-2009
25 Cruiser Bidarka II 2010-2013
38 Trawler Mia Terra 2012-2015
42 Nordic Tug 2015-
28 KingFisher 2009-2014
14 Jetcraft 2000-
17 Scanoe 1981-
Back to top
View user's profile Send private message Send e-mail
thataway



Joined: 02 Nov 2003
Posts: 20779
City/Region: Pensacola
State or Province: FL
C-Dory Year: 2007
C-Dory Model: 25 Cruiser
Vessel Name: thataway
Photos: Thataway
PostPosted: Mon Aug 24, 2009 11:37 am    Post subject: Reply with quote

At least in the Tom Cat, it makes little difference in top speed or fuel economy. In this boat it runs on the surface. In the C Dory, it was under water, so i suspect a little drag, BUT, it got the boat on plane faster and my feeling was the fuel economy was better--speed about the same.
_________________
Bob Austin
Thataway
Thataway (Ex Seaweed) 2007 25 C Dory May 2018 to Oct. 2021
Thisaway 2006 22' CDory November 2011 to May 2018
Caracal 18 140 Suzuki 2007 to present
Thataway TomCat 255 150 Suzukis June 2006 thru August 2011
C Pelican; 1992, 22 Cruiser, 2002 thru 2006
Frequent Sea; 2003 C D 25, 2007 thru 2009
KA6PKB
Home port: Pensacola FL
Back to top
View user's profile Send private message Send e-mail
Wandering Sagebrush



Joined: 21 Jan 2005
Posts: 2768
City/Region: Northeast Oregon
State or Province: OR
C-Dory Year: 2005
C-Dory Model: 22 Cruiser
Vessel Name: Constant Craving
Photos: Constant Craving
PostPosted: Mon Aug 24, 2009 12:00 pm    Post subject: Permatrim - Fuel Consumption Reply with quote

Tom,

I don't believe that I am seeing any great jump in fuel consumption with my boat. We have a Honda 90 with carburetors. I typically run (light load, full of fuel) at around 4200-4400 rpm and 20-22 mph when water conditions permit. WOT is around 5400+ for me, and I was surprised to see it hit 31mph when I cleared the bar into Tillamook Bay a couple of weeks back. On that trip, we were offshore for about 6 hours, probably ran 8-9 miles each way in moderate chop, and trolled all day on the 90. My guess is that I burned between 6 and 7 gallons of fuel.

I'll let you know about loaded cruise (and altitude effect) after the Lake Powell trip.

Steve

_________________
"And in the end, it's not the years in your life that count. It's the life in your years." - Abraham Lincoln
Back to top
View user's profile Send private message
20dauntless



Joined: 23 Jan 2008
Posts: 879
City/Region: Mercer Island and Decatur Island
State or Province: WA
C-Dory Year: 2008
C-Dory Model: 22 Cruiser
Vessel Name: Retriever and Nordic Tug 37
Photos: Retriever
PostPosted: Mon Aug 24, 2009 12:47 pm    Post subject: Reply with quote

Steve, Tom and I (and others I'm sure) have the EFI Honda 90, also known as the BF90D. This engine has all sorts of Honda technology like VTEC, BLAST, and Lean Burn Control. My belief is that at some point (based on load and RPM) the computer changes the timing fuel map and requires more fuel.

That being said, this is an excellent engine. It's smooth, quiet, starts instantly, and has no problem pushing the C-Dory even when loaded very heavily.
Back to top
View user's profile Send private message Visit poster's website
BaseCampAnne



Joined: 04 Nov 2007
Posts: 169
City/Region: San Diego/Anacortes
State or Province: WA
C-Dory Year: 2008
C-Dory Model: 22 Cruiser
Vessel Name: SEA COASTER
Photos: SEA COASTER
PostPosted: Mon Aug 24, 2009 11:28 pm    Post subject: hydrofoil Reply with quote

Back to the original question...I got one of these on the advice of Don Anderson of the Jenny B. Thanks, Don!

I have learned that it is very strong and have heard in a Coast Guard Auxiliary class that it can be used in an emergency (when the engine is OFF) to help with getting someone out of the water, or at least somewhat higher when trying to recover someone from the back of the boat. I don't think Gus, my lab, will find it useful, but someone with very little upper body strength can stand on it and find it useful to be lifted up out of the water a bit....

Anne Cox (in the process of joining the retired and wondering how to pay for everything) Question Exclamation
Back to top
View user's profile Send private message Send e-mail
tpbrady



Joined: 08 Feb 2005
Posts: 891
City/Region: Anchorage
State or Province: AK
C-Dory Year: 2005
C-Dory Model: 25 Cruiser
Vessel Name: Bidarka II
Photos: Bidarka
PostPosted: Mon Aug 24, 2009 11:49 pm    Post subject: Reply with quote

If you look at many of the prop test reports on Honda's web site, you will see a steep increase in fuel consumption occurring between 3900 and 4400 rpm on the BF90D versus a linear fuel curve for the BF90A. I really think they need to work on software to smooth it out some.
Back to top
View user's profile Send private message Send e-mail
thataway



Joined: 02 Nov 2003
Posts: 20779
City/Region: Pensacola
State or Province: FL
C-Dory Year: 2007
C-Dory Model: 25 Cruiser
Vessel Name: thataway
Photos: Thataway
PostPosted: Tue Aug 25, 2009 12:20 pm    Post subject: Reply with quote

Fuel consumption is related to HP output. If the fuel consumption is going up, so is the HP--often max HP is at top RPM. There can be all sorts of things going on--more injector pressure, different timing of injection and valves. I suspect that you are having more effecient use of the engine at mid to high RPM, then at max RPM the fuel consumption goes up.

Unfortunately outboard manufactuers don't often post RPM/Fuel/Torque and fuel consumption curves. Just prop test curves can be miss leading because of the dynamics, of the boat hull, prop interaction and drag factors as the speed increases. Boat speed and HP are not linlear functions.
Back to top
View user's profile Send private message Send e-mail
Display posts from previous:   
Post new topic   Reply to topic    The C-Brats Forum Index -> Trims Tabs, Hydrofoils All times are GMT - 5 Hours
Goto page Previous  1, 2
Page 2 of 2

 
     Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You cannot download files in this forum



Page generation time: 0.0854s (PHP: 84% - SQL: 16%) - SQL queries: 25 - GZIP disabled - Debug on