Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 07-08-2013, 22:51   #16
Senior Cruiser
 
Wanderlust's Avatar

Cruisers Forum Supporter

Join Date: Aug 2005
Location: NSW Central Coast
Boat: Lagoon 410
Posts: 499
Re: Is a 9.9 outboard enough for a 38 foot boat?

A 9.9 hp should be OK most of the time, and you get the advantage of being able to swivel it for sideways thrust and better manouverability. That's the positive part.

But designing a solution for "most of the time" could be a bit dangerous. What happens when you need to bash into a strong wind or a strong tidal channel? I would be surprised if a 9.9 hp would be sufficient.

You said you wanted to mount an outboard like on your current boat. Does this mean you are not constrained to your existing 9.9hp?

Then there is the question of any outboard hanging off the stern of a sailboat. The stern typically has a lot more movement than a power boat, so it won't take much of a sea to have the prop repeatedly spinning in air.

My suggestion is that the outboard solution would be OK for temporary use while you sort out a proper solution. Just be mindful of its limitations.

Then of course some people have no engine and yet manage OK.
__________________

__________________
Steve
Wanderlust is offline   Reply With Quote
Old 08-08-2013, 00:31   #17
Senior Cruiser

Cruisers Forum Supporter

Join Date: Dec 2006
Location: Seattle
Boat: Cal 40
Posts: 2,401
Images: 7
Re: Is a 9.9 outboard enough for a 38 foot boat?

Interesting how rules of thumb change over time.

Cruising Under Sail, Eric Hiscock:

"For normal cruising purposes one horsepower per ton of displacement should be sufficient - Wanderer IV (22 tons) requires no more than 18 horsepower to give her a speed of 5 1/2 knots in quiet weather. But if the yacht is to be capable of making good progress against a headwind and sea, or to reach her maximum hull speed under power (some owners feel this is essential) at least 3 horsepower per ton will be required."


Previously posted was 1 hp per 500 lbs, which is 4 hp per 2000 lbs. Hiscock probably means long tons so about 4.5 hp per ton is the current recommendation.

Don't follow the old rule of thumb if you expect to motor at hull speed directly into 25 knot head winds.

Old rule of thumb doesn't seem to be entirely dead:
Horse Power per ton?

My boat is about 3.3 hp per ton. Works for me.
__________________

__________________
cal40john is offline   Reply With Quote
Old 08-08-2013, 01:29   #18
Registered User

Join Date: Nov 2007
Location: Probably in an anchorage or a boatyard..
Boat: Ebbtide 33' steel cutter
Posts: 3,540
Past few passages I've used a 15hp Honda outboard on the back of a 33' 10t long keel. Stationary into a bit of breeze and a chop but moves it in flat calm. Costs more in fuel as well. And no alternater for nav lights at night. Not something I'd do by choice.
__________________
conachair is offline   Reply With Quote
Old 08-08-2013, 02:09   #19
Registered User
 
Tomm0's Avatar

Join Date: Jan 2013
Location: Melbourne, australia
Boat: Joubert Koala 24
Posts: 114
Re: Is a 9.9 Outboard Enough for a 38 Foot Boat?

Go for an electric drive inboard!
I don't have one, never seen one actually going, etc, but the idea really appeals.
__________________
Tomm0 is offline   Reply With Quote
Old 08-08-2013, 03:00   #20
Registered User

Join Date: Nov 2011
Location: The Netherlands
Boat: Baltic 38DP
Posts: 333
Re: Is a 9.9 outboard enough for a 38 foot boat?

Quote:
Originally Posted by cal40john View Post
Previously posted was 1 hp per 500 lbs, which is 4 hp per 2000 lbs. Hiscock probably means long tons so about 4.5 hp per ton is the current recommendation.

My boat is about 3.3 hp per ton. Works for me.
Mine is 27bhp for a 38 footer, displacement 6.5 tonnes. Works out as 4.1 bhp per tonne, or 3.76bhp per ton. I think that works OK, but these days people would probably put more in.

I would never use an outboard to maneuver a 8 tonne 38 footer, no matter how much hp it has, especially when shorthanding. But then I'm tight marinas all the time, in other situations you might be able to make it work.


Onno
__________________
JazzyO is offline   Reply With Quote
Old 08-08-2013, 03:03   #21
Registered User

Join Date: Nov 2011
Location: The Netherlands
Boat: Baltic 38DP
Posts: 333
Re: Is a 9.9 Outboard Enough for a 38 Foot Boat?

Quote:
Originally Posted by Tomm0 View Post
Go for an electric drive inboard!
I don't have one, never seen one actually going, etc, but the idea really appeals.
I think that will be a very expensive solution, judging by the cost of Torqueedo's. I'm also not sure it works well if you motor a lot. If you don't, then it might work but you still need serious recharging facilities.

I like the fact that my diesel is an onboard generator. With solar panels and a windgen you have 3 ways of getting juice in the batteries. With an electric inboard you only have 2, and you've lost the most powerful charger.


Onno
__________________
JazzyO is offline   Reply With Quote
Old 08-08-2013, 03:16   #22
Registered User
 
Tomm0's Avatar

Join Date: Jan 2013
Location: Melbourne, australia
Boat: Joubert Koala 24
Posts: 114
Re: Is a 9.9 Outboard Enough for a 38 Foot Boat?

I have an 8hp outboard but I only displace a couple of tonnes.
And the outboard pushes 5A into my battery when the sun is lacking on my panels.
__________________
Tomm0 is offline   Reply With Quote
Old 08-08-2013, 04:22   #23
Marine Service Provider

Cruisers Forum Supporter

Join Date: May 2013
Location: UK,Portugal
Boat: 78ft ex racing catamaran
Posts: 67
Re: Is a 9.9 Outboard Enough for a 38 Foot Boat?

Quote:
Originally Posted by JazzyO View Post
I think that will be a very expensive solution, judging by the cost of Torqueedo's. I'm also not sure it works well if you motor a lot. If you don't, then it might work but you still need serious recharging facilities.

I like the fact that my diesel is an onboard generator. With solar panels and a windgen you have 3 ways of getting juice in the batteries. With an electric inboard you only have 2, and you've lost the most powerful charger.


Onno
I think the suggestion was to go for electric inboard not torqueedo electric outboard and it seems like a very sensible solution when faced with the need to install or replace an inboard engine.

As I understand it the electric motor power output requirements for a yacht are less than what would be required for a diesel engine because you have maximum thrust at 1rpm and can use larger diameter props at lower revs for increased trust.

Given OP boat is ~8.5 ton @ 2HP per ton == 17HP minimum requirement

1 HP == 0.74 KW thus 12.5KW is minimum requirement

Agni motors 95 model will output 12.5KW continuously at 56V with 5sec bursts of 22KW. The 95-R model will output 16KW continuously at 78V with 5sec bursts of ca. 30KW.

As has been stated previously the HP of an inboard engine is at the engine not at the prop whereas almost 100% of the power output of the electric motor is delivered to the prop. Furthermore if more power on a single prop is required I think 2 motors can operate in tandem with a system of pulleys and belts.
__________________
damianham is offline   Reply With Quote
Old 08-08-2013, 04:26   #24
Registered User

Join Date: Oct 2012
Location: nelson new zealand
Boat: kuiper 32
Posts: 198
Images: 3
Re: Is a 9.9 Outboard Enough for a 38 Foot Boat?

I know of quite a few 28 to 32 footers around here with 10 hp diesels in them most of them are not powerful enough in any type of head sea or wind.So I cant see how a 10 hp would push a bigger boat.I would want at least 30 hp to feel happy coming into a marina full of expensive boats,or when anchor is dragging on a lee shore.
__________________
builder dan is offline   Reply With Quote
Old 08-08-2013, 04:31   #25
Registered User

Join Date: Apr 2012
Location: Pittsburgh
Boat: Albin Vega 27
Posts: 23
Re: Is a 9.9 Outboard Enough for a 38 Foot Boat?

Thanks everyone for your thoughts. I am going to give it a shot and see how it works out. I will pass along my experience in a few weeks.
__________________
subquanta is offline   Reply With Quote
Old 08-08-2013, 05:07   #26
Armchair Bucketeer
 
David_Old_Jersey's Avatar

Join Date: Oct 2006
Posts: 10,013
Images: 4
Re: Is a 9.9 Outboard Enough for a 38 Foot Boat?

Quote:
Originally Posted by subquanta View Post
Thanks everyone for your thoughts. I am going to give it a shot and see how it works out. I will pass along my experience in a few weeks.
Please do (it all goes into the pot of knowledge ), some pics of the installation (and boat) would also be useful.

FWIW, me is in the camp of yes!, it will be enough - just not for all of the time. How much time and how much that matters is purely down to how you choose and have to use the boat (and engine).

Am guessing that financial is the reason for the o/b choice, if my use and location allowed (i.e. not a Marina 5 miles up a river) and I really liked the boat (in design, condition and price!) me would go for the o/b as a temporary solution (even if in years!) and then either save the pennies for an inboard or for electric power (or at least have a very long hard look - from my early investigations seems that the installation can develop as budget allows).

Of course as you know, no working inboard knocks the stuffing out of the value of a boat, especially when they get older.
David_Old_Jersey is offline   Reply With Quote
Old 08-08-2013, 13:21   #27
Senior Cruiser
 
SkiprJohn's Avatar

Cruisers Forum Supporter

Join Date: May 2006
Location: Kea'au, Big Island, Hawaii
Boat: Cascade, Sloop, 42 - "Casual"
Posts: 14,192
Re: Is a 9.9 outboard enough for a 38 foot boat?

Quote:
Originally Posted by cal40john View Post
Interesting how rules of thumb change over time.

Cruising Under Sail, Eric Hiscock:

"For normal cruising purposes one horsepower per ton of displacement should be sufficient - Wanderer IV (22 tons) requires no more than 18 horsepower to give her a speed of 5 1/2 knots in quiet weather. But if the yacht is to be capable of making good progress against a headwind and sea, or to reach her maximum hull speed under power (some owners feel this is essential) at least 3 horsepower per ton will be required."


Previously posted was 1 hp per 500 lbs, which is 4 hp per 2000 lbs. Hiscock probably means long tons so about 4.5 hp per ton is the current recommendation.

Don't follow the old rule of thumb if you expect to motor at hull speed directly into 25 knot head winds.

Old rule of thumb doesn't seem to be entirely dead:
Horse Power per ton?

My boat is about 3.3 hp per ton. Works for me.
9.9 is plenty enough power. It's the height and depth in a seaway which might get you in a bit of trouble. Each wave will either put your powerhead underwater or your prop out of the water. I can't wait to see your success.

Current rated hp for inboards is way out of whack. I've seen the Perkins 4-108 rated at 50 hp or 36 hp depending on who you talk with. More honestly it should be rated at 20-25 because most folks don't rev them to 3600 rpm.
__________________
John
SkiprJohn is offline   Reply With Quote
Old 08-08-2013, 13:41   #28
Senior Cruiser
 
Cheechako's Avatar

Cruisers Forum Supporter

Join Date: Aug 2006
Location: Skagit City, WA
Posts: 19,369
Re: Is a 9.9 outboard enough for a 38 foot boat?

Quote:
Originally Posted by SkiprJohn View Post
9.9 is plenty enough power. It's the height and depth in a seaway which might get you in a bit of trouble. Each wave will either put your powerhead underwater or your prop out of the water. I can't wait to see your success.

Current rated hp for inboards is way out of whack. I've seen the Perkins 4-108 rated at 50 hp or 36 hp depending on who you talk with. More honestly it should be rated at 20-25 because most folks don't rev them to 3600 rpm.
Yeah, they are often rated according to usage also... or maybe I should say Derated.... Interestingly a 4-108 pushed my heavy 44 footer very well in all conditions and my max rpm was 2800. Thinking back you would think it was a little meager for that boat. The Yanmar 3QM30 in the HC 38 in my avatar didnt push the boat well at all. 27500 lb dry weight + 2500lb for excess / 30 hp (max) would be about 1000 lbs per HP. Not near enough.
__________________
"I spent most of my money on Booze, Broads and Boats. The rest I wasted" - Elmore Leonard











Cheechako is offline   Reply With Quote
Old 08-08-2013, 20:45   #29
Registered User

Join Date: Jun 2010
Location: Easton, MD
Boat: Catalina 22 Capri
Posts: 1,054
Re: Is a 9.9 Outboard Enough for a 38 Foot Boat?

NO!!!!!!!!!!!!
__________________

__________________
kmacdonald is online now   Reply With Quote
Reply

Tags
outboard

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Girl Overboard ! TigerLilly Health, Safety & Related Gear 82 24-02-2016 23:07
Honduras: Sailing Boat Boarded and Robbed by Pirates foolishsailor Health, Safety & Related Gear 391 25-09-2015 08:20
For Sale or Trade: 565+ Nautical E-Books Crimea Cruiser Classifieds Archive 10 23-06-2013 21:33
OpenCPN Release Candidate Version 3.1.1411 Released bdbcat OpenCPN 48 24-02-2013 07:59
Hmmmm - Bowthrusters ?? CnC40sailor Monohull Sailboats 193 31-08-2012 09:55



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 10:56.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.