User Tag List
Results 1 to 15 of 27
Thread: Outboard height with setback
-
02-21-2020, 09:13 AM #15000 RPM
- Join Date
- Nov 2013
- Location
- Florida
- Posts
- 121
- Thanks (Given)
- 0
- Thanks (Received)
- 6
- Likes (Given)
- 0
- Likes (Received)
- 15
- Mentioned
- 0 Post(s)
- Tagged
- 0 Thread(s)
Outboard height with setback
Yes I have used the search function. The general rule is 1” per 12” set back. Well my outboards are 1.75” up from the bottom at a 24” setback. It’s a 23ft boat, 24 degree bottom with a small pad and twin 250 merc efis in 30” shaft length. The boat porpoises like crazy and it’s hard to handle. Will moving them up another 2” for a total of roughly 4” up help or hurt?
I’m about to fabricate some simple vertical jack plates from 1/2” angle aluminum and I’m debating if it’s worth my time and effort. Yes the bracket and transom can take the additional load, it’s all been way overbuilt over the years of previous repairs.
-
02-21-2020, 09:32 AM #2
-
02-21-2020, 09:38 AM #35000 RPM
- Join Date
- Nov 2013
- Location
- Florida
- Posts
- 121
- Thanks (Given)
- 0
- Thanks (Received)
- 6
- Likes (Given)
- 0
- Likes (Received)
- 15
- Mentioned
- 0 Post(s)
- Tagged
- 0 Thread(s)
The cav plate is exactly 1.75” from that point of the hull bottom. So to clarify, where the centerline of the outboard hits the v bottom, that point is exactly 1.75” lower then the outboards cavitation plate.
the outboards are at the v portion of the hull which is just a strait 24 degrees, no variable deadrise or anything funky. The pad may be 5” wide and 14” long, it’s not muchLast edited by chevy355mark; 02-21-2020 at 09:41 AM.
-
02-21-2020, 10:18 AM #45000 RPM
- Join Date
- Nov 2013
- Location
- Florida
- Posts
- 121
- Thanks (Given)
- 0
- Thanks (Received)
- 6
- Likes (Given)
- 0
- Likes (Received)
- 15
- Mentioned
- 0 Post(s)
- Tagged
- 0 Thread(s)
-
02-21-2020, 11:10 AM #5
Difficult to see your engine height from the picture angle, but it appears that your engines are mounted quite low. Raising will probably help susceptibility to porpoising.
Note: Lower Unit height is best measured with reference to the CL of the 'bullet' or 'torpedo', not the cavitation plate, since thrust comes from propeller shaft, not the cavitation plate. Height is the measure to local planing bottom surface.
Also: see article on 'Porpoising' which may be of help.Last edited by Jimboat; 02-21-2020 at 12:42 PM.
-
Glasstream15 liked this post
-
02-21-2020, 12:08 PM #65000 RPM
- Join Date
- Nov 2013
- Location
- Florida
- Posts
- 121
- Thanks (Given)
- 0
- Thanks (Received)
- 6
- Likes (Given)
- 0
- Likes (Received)
- 15
- Mentioned
- 0 Post(s)
- Tagged
- 0 Thread(s)
So where should my nose cone cl fall then? Even with the bottom of the V?
if I’d benefit from a full 5” up I’ll have the shafts cut and go conversion. Anything less and I’ll do the adapter route as I don’t want the motors any lower to the water
-
02-21-2020, 12:43 PM #7
try higher using small increments. watch for sufficient water/cooling pressure. So where is your nose cone CL now?
Also check out articles on 'Porpoising' and 'Boat Static Balance' and 'Dynamic Stability'Last edited by Jimboat; 03-03-2020 at 06:07 PM.
-
02-21-2020, 05:51 PM #85000 RPM
- Join Date
- Nov 2013
- Location
- Florida
- Posts
- 121
- Thanks (Given)
- 0
- Thanks (Received)
- 6
- Likes (Given)
- 0
- Likes (Received)
- 15
- Mentioned
- 0 Post(s)
- Tagged
- 0 Thread(s)
the nosecones center is is 8" away from the cav plate making them 6.25" below the local vee surface.
-
02-21-2020, 10:20 PM #9
A good rule of thumb is to get prop shaft 3 1/2in below pad( running suface) then watch pressure , its seems to work great for starting point with no low water pick up, even with pad will be to high and low.water pressure
-
02-21-2020, 11:45 PM #10Screaming And Flying!
- Join Date
- Feb 2015
- Location
- Ontario
- Posts
- 8,091
- Thanks (Given)
- 205
- Thanks (Received)
- 321
- Likes (Given)
- 1921
- Likes (Received)
- 2005
- Mentioned
- 2 Post(s)
- Tagged
- 0 Thread(s)
Can you remove 5" extensions from those legs and machine the drive shafts then drop down a hole or two ? Every time I see those monsters I lose count of cav plates.
Is that an old stepside?Last edited by FMP; 02-21-2020 at 11:49 PM.
-
02-22-2020, 07:32 AM #115000 RPM
- Join Date
- Nov 2013
- Location
- Florida
- Posts
- 121
- Thanks (Given)
- 0
- Thanks (Received)
- 6
- Likes (Given)
- 0
- Likes (Received)
- 15
- Mentioned
- 0 Post(s)
- Tagged
- 0 Thread(s)
These have low water pickups anyway. I’ll get out there and really do some more accurate measurements. I really don’t want them any lower. If they were 2.5s I’d say no way do I want them up in the air but these are pretty heavy and the boat squats really deep coming off plane especially in rough seas or running a heavy following sea.
FMP, that’s an 86 narrow frame dually with a step side bed. These 1998 outboards are sadly the newest piece of equipment I own... by quite a bit lol
-
02-22-2020, 08:37 AM #12
-
02-22-2020, 09:19 AM #13
Did you buy the boat set up like this or did you just put the motors on?. Take a 2x4 and lay it up against the hull and side it out til it hits the drive and see where the top of the 2x4 hits the drive with the drives all the way down. Seems if they where to low they would be driving the bow down. JMO.. Could also need a bigger dia prop for your application.
I have my motors high. It only takes a couple bumps of the trim switch to trim, than one more and she starts to porpoises.
-
02-22-2020, 09:24 AM #14Screaming And Flying!
- Join Date
- Feb 2015
- Location
- Ontario
- Posts
- 8,091
- Thanks (Given)
- 205
- Thanks (Received)
- 321
- Likes (Given)
- 1921
- Likes (Received)
- 2005
- Mentioned
- 2 Post(s)
- Tagged
- 0 Thread(s)
If powerhead height off plane and trolling in good swells then yeah otherwise the shorter leg etc but it looks from here if the 5" spacer was out of the leg lowers could be a lot closer to good height +/- a hole.
Need two 25" shafts and water tubes etc.
Going to look high up.
86 !Last edited by FMP; 02-22-2020 at 05:55 PM. Reason: Yup lost count to 30" again
-
02-24-2020, 04:50 PM #155000 RPM
- Join Date
- Nov 2013
- Location
- Florida
- Posts
- 121
- Thanks (Given)
- 0
- Thanks (Received)
- 6
- Likes (Given)
- 0
- Likes (Received)
- 15
- Mentioned
- 0 Post(s)
- Tagged
- 0 Thread(s)
I’m starting to lean towards doing the 25” conversion the more I look at it and thing about it. I’ll post the final product once I pull the trigger
Similar Threads
-
setback vs height
By ultrafast in forum Props, Setup, and RiggingReplies: 3Last Post: 09-29-2013, 02:05 PM -
Mercury Tech: Engine setback and height?
By superboat24michael in forum Technical DiscussionReplies: 7Last Post: 07-07-2010, 07:06 AM -
setback and motor height
By Sinister in forum Props, Setup, and RiggingReplies: 14Last Post: 03-19-2008, 07:53 PM -
Twin eng. setback to height?
By Racemore in forum Technical DiscussionReplies: 8Last Post: 02-26-2003, 04:31 AM -
Setback vs engine height
By WATERWINGS in forum Technical DiscussionReplies: 4Last Post: 02-11-2003, 06:12 PM