Transom Bracket - twin outboards
 

Must be a few of you guys running twins off of a bracket??

My boat, new to me this spring, is a 78 23' CC totally rebuilt with an Armstrong bracket and twin 2008 Yamaha F-150s.

Sounds nice - looks nice .....runs like crap(in rough water).

The props get air, they slip, the rpms spike etc - whenever in a heavy chop.
I put hydrofoils on both motors and they are nice but I still have most of the problem in rough water - we have heavy chop mixed with our swells here in Michigan.

Today I had the motors lowered to the last hole (down) and will run it tomorrow to see if it is any help.

Anybody else have any issues like this? Anybody run a jack plate to lower the motors DEEP after getting out of the hole (in the chop) -

anybody have any suggestions at all? I have inquired several prop experts and they feel that all props will slip to a certain extent with this bracket/twin setup until I fix the underlying problem...

Thanks in advance -

Steve

Re: Transom Bracket - twin outboards
 

What is the underlying problem the "prop experts" warn you about??

Re: Transom Bracket - twin outboards
 

well - I have very limited experience in this arena and am open to any and all advice (to consider) but what I have been told by some prop people is that in choppy seas .............

"It sounds like you are probably pulling surface air into the props in the chop. This can be a common problem during certain wave conditions, and it more prevalent with bracket mounted motors or stepped hull designs that tend to pull air under and channel it back to the prop"......if that is the case, going to a 4 blade prop won't make a difference, it will slip the same way...."

just a few excerpts -

any thoughts?

Re: Transom Bracket - twin outboards
 

I run twin F150's on a twin bracket as well and have no problems. I have fished the boat in some nasty weather and have never had the props slip at all. I was thinking it may be a prop issue, but sounds like it may be something else. What length are the shafts? Could the bracket be mounted too high? Could the bracket be mounted too low?

Re: Transom Bracket - twin outboards
 

Wow! BA17 Glad to see you chime in here!!!! maybe you and I could compare a little information.

This boat I bought is wayyyy too nice to not be able to enjoy the ride in rough water! As it stands now - I can only run about 18 mph in the slop w/o prop issues.

Let me see what I have tomorrow with the motors lowered to the last hole and then if need be - I could compare your specs to mine????

Re: Transom Bracket - twin outboards
 

Been there & done that. For years I ran a 1972 23' with twin 200 HP OX66's (see below picture). Also, it had an enclosed transom and a full flotation bracket.

I have the following questions for you:

Does the boat sit stern heavy in the water?

Do you have any balast materials up front?

What type of props are you using?

What kind of trim tabs are you using, and are you sure that they are properly working?

Have you checked your bracket to see if she has any water leaking into her?


Here is what I did with my set-up to get her dialed in.

I put 200 pounds of lead up front in the bow hatch

I had the engines mounted in the mid level setting on the bracket.

When the engines were at the highest level setting my 3 blade 19 pitch & 15.25 sws props were capable of coming out the water. When I put on 21 x 14, 7/8 props they did not come out of the water anymore.

SeaCraft's with brackets and alot of engine weight need alot of trim tab. I had 16 x 12 Bennett sportman trim tabs. I was not happy with their performance initially. I pulled the boat of the water and saw that the tabs were not working that well. It ended up being that I was a little low in transmission fluid. When I filled the system up, I had far more responsive tabs and a better handling boat.

I eventually went to 4 blade power tech props. They gave me decent stern life and improved the boat handling. My speed at WOT went down from 56 MPH to about 47 MPH, but I was happy with the trade-off.

If you have any specific questions, please let me know.

Regards,

Peter

Re: Transom Bracket - twin outboards
 

sounds more like a prop problem. I run my motors real high
on my bracket without breaking loose.get someone to run the boat and while running check and see where your cav plates are in the water with my 250's I had to run an inch and a half up above the water to get out of the hole. my 150's
run right on the surface also look to see if a transducer or somthing is making some problems.Also the gulf down her gets real sloppy.

Re: Transom Bracket - twin outboards
 

I agree that you have a prop problem. But I'll also bet you need your whole setup tuned.

Do this test: With the motors trimmed fully down, with no trim tabs in use, while at about 4000 rpms, turn the boat sharply left and right, as sharply as you can. If you get the outside prop ventilating in the turn, you've also got a mounting height problem, for either the motors, or the bracket, or both. (This test assumes factory-cupped propellers.)

Let us know.

Re: Transom Bracket - twin outboards
 

lots of good info here. will print it out and post tonight or tomorrow morning with results on my trial from today.

i have added 90 pounds of lead to the front to see if it made any difference. I didnt notice too much..... I dont think it sits stern heavy but I will take a few pictures and get your opinion.....no water comes in the scuppers with me in the back sitting at the dock.

where the motors were mounted until today and with my last setup - my boat pretty much jumped on plane. I put the throttles down all the way and would maybe get 6-8" of bow lift......this is after adding the hydrofoils.

lots of variables here to work out but at least I have some guys here that have some experience with this very issue and I am optimistic it will work out.

thank you all

Re: Transom Bracket - twin outboards
 

Lobo, Post a couple of pictures from different distances of the stern kind of parallel to keel. I would like to see where the cav plates/tabs are in relation to everything.

Re: Transom Bracket - twin outboards
 

no luck on the dropping of the motors to the lowest hole - may even be worse. had 25 mph winds so it was too choppy to do too much of a trial but it I was out long enough to figure out this is not the correct setup. I also put my 300 pound son along with my wife and daughter in the bow and this is not helping.
My trim tabs appear to be 12x12 and working fine. There is nothing dragging under my boat - the transducer shoots thru hull - I am pretty sure the motors are dragging tho.
I have added a bunch of pictures to my photobucket that I took yesterday the links are below.
I appreciate any feedback.
4 photos are of the boat at rest in the water with motors all the way down- I have on board 90 pounds of lead in the bow, 100 gals of fuel, 3 batteries, and a cooler with drinks.
I have some others pics of the props themselves, and how the motors are mounted etc with them all the way down and on the trailer.

http://i962.photobucket.com/albums/a...s/IMG_0436.jpg
http://i962.photobucket.com/albums/a...s/IMG_0437.jpg
http://i962.photobucket.com/albums/a...s/IMG_0438.jpg
http://i962.photobucket.com/albums/a...s/IMG_0439.jpg
http://i962.photobucket.com/albums/a...s/IMG_0435.jpg
http://i962.photobucket.com/albums/a...s/IMG_0428.jpg
http://i962.photobucket.com/albums/a...s/IMG_0427.jpg
http://i962.photobucket.com/albums/a...s/IMG_0426.jpg
http://i962.photobucket.com/albums/a...s/IMG_0425.jpg
http://i962.photobucket.com/albums/a...s/IMG_0424.jpg
http://i962.photobucket.com/albums/a...s/IMG_0429.jpg
http://i962.photobucket.com/albums/a...s/IMG_0431.jpg
http://i962.photobucket.com/albums/a...s/IMG_0432.jpg
http://i962.photobucket.com/albums/a...s/IMG_0433.jpg
http://i962.photobucket.com/albums/a...s/IMG_0434.jpg


thanks in advance!
Steve

Re: Transom Bracket - twin outboards
 

Put a straight 2x4 along the hull bottom directly in front of the lower unit to see where the cavitation plate sits in relation to the hull bottom.

It's hard to tell from your photos, but if it is as it appears, I'd say you're mounted with your cavitation plates almost dead even with the hull bottom, and that's about 3 to 4 inches too low. Your cavitation problem in turns would then be (in part) a result of having your cavitation plate causing excessive turbulence from running too deep.

Use the straight 2x4 as a straight edge along the hull back to the lower unit, and, with your engines at neutral trim, put the engines where the cavitation plate is about 3" to 3 1/2" above the straight edge. That's usually a pretty good starting place.

Hopefully Peter B will chime in about where his were mounted.

Re: Transom Bracket - twin outboards
 

IMHO....
In this picture
http://i962.photobucket.com/albums/a...s/IMG_0425.jpg it looks like the motors are reverse trimed. If you take a look at the boot strap, and put a ruler on the picture, it looks like the motors are angled in, underneath the boat. I have been on a couple of boats with yammie 4 strokes that had similar problems, and they required "wedges" to correct the condition. The energy of the prop is pushing up, and pushing the back of the boat up. This is causing cavitation, as the props push the stern up, when you come off a wave, it cavitates, drops back down, and then catches water again.

I think yammie did this on purpose to overcome the additional weight of the 4 strokes, to get the boats on plane faster, so they reverse angle it. Once you get on plane, try trimming up some and see if it helps keep it in the water. The bow should get lighter, and the stern should stay in the water better. I bet this rig is a handfull in a following sea set up like that.

It is really hard to set the height from a picture, but I am pretty sure your motors are too low, not too high. You might want to talk to armstrong, they were helpful when I was setting mine up. BTW, the water comes up about a little over an inch for every 12"'s of setback on the motor.

Put a straight edge on the bottom of the hull extending back, and I would mount the cavitation plates 2.5"'s above that line.

Re: Transom Bracket - twin outboards
 

I agree, they look too low. I would try raising them, remove the foils,and work with someone on props to dial it in. The 4 blade has helped mine.

Re: Transom Bracket - twin outboards
 

will take a straight board and a level with me tomorrow and then have them raise them up. Will take one hole up just to get it back to where it was - so I will either go two or all 3 holes up this time.

it is a bear in a following sea. i am not comfortable with it at all - makes me a bit nervous actually..... :(

one of my favorite spots to fish this time of year is about 19 miles offshore in Lake Michigan - I cant go out there with this boat like it is.

Re: Transom Bracket - twin outboards
 

IMHO, the motors are lifting the stern up and driving the nose into the water coming off from following seas. I was on a contender that used to do this, he put wedges in, raised the motor up, and it made a world of difference. The way you have them also will suck a lot of gas.

Get those motors at the right height, and than use your trim to get the motors into a neutral, vs negative trim state. It would really help to have someone drive the boat so you can look at the cavitation plates. If you can, shoot some pictures looking down at the plate while it is running.

Re: Transom Bracket - twin outboards
 

I will have the motors raised up a few holes - I can trim the motors to neutral. For 70 bucks I'll certainly add the wedges but cant seem to make my brain understand the additional benefit I will gain - above and beyond trimming the motors to a neutral position.

thanks again,

steve

Re: Transom Bracket - twin outboards
 

It's my undertanding the wedges were designed (unless mounted upside down) to increase negative trim, which you appear to have plenty.

Re: Transom Bracket - twin outboards
 

I think wedges can go either way, negative or positive. I am not an expert on them. The boat I am thinking of was an older 31 contendor with 225 4S yammies, and I remember looking at it on the trailer and the motors looked like these, tucked under the bracket. I think he installed something that when the motor were trimmed down, they would be in a neutral vs negative trim state.

The idea is that when the motors are trimmed all the way down, the motors will have a neutral trim, in that the cavitation plates are paralell to the water they are running through. The water coming off the back of that boat is not flat, it is angled up about 10 or so degrees, or at least it was on mine. I moved my motor up and down on that bracket serveral times, and played with the trim to get it right.

Obviously, start by running with the trimmed up so that the cavitation plates are paralell to the water. This is hard to do without 2 people. I used a camera to shoot pictures of where the water was hitting. The key is to get the height in the ball park, then dial in the trim. I would start by using a straightedge off the bottom to the cavitation plate, and mount the motors so the cavitation plates are at least 2"'s above that line.

Re: Transom Bracket - twin outboards
 

Lobo, You got me thinkin'....

My single (on aluminum 30" setback bracket) cavitation plate is 3" above keel. This mounted in top bracket hole, 2nd hole down on motor.



Looking at your pictures and thinking here, I believe your foils are acting like sails against the water when coming off a wave and preventing the motors to go "under" water momentarily, allowing the props to have little or no water to "bite". I believe setting the cav plates correctly, removing the foils, adding (or changing) to a cupped prop (and probably 4 blades) will help tremendously.

One more afterthought....

I had the pleasure of running a 23' Triton w/twin 150 HPDI's for a few seasons. Those motors ran best when mounted "goofy foot", opposite of yours.

Re: Transom Bracket - twin outboards
 

I think John is dead on about the negative trim - you have excess and that need a way to govern that, wedges or a 2x4 - whatever keeps your prop shaft and cavitation plate mostly parallel to your keel. Like Dana Carvey mimicking Uncle George Sr., "Don't want to be \ nor / wanna be somewhere in between, sure..." ;)

Fr. Frank's suggestion on measuring engine height is very important. Straight edge on bottom of hull in line with each motor skeg and cavitation plate parallel to hull bottom. Seacrafts run best with cav plate about an 1-1/2" above the hull bottom, additionally, Armstrong asks for 1" of rise for every foot of bracket setback...you do the math.

Finally, I'm with reelescape - ditch the foils. Use the the trim tabs for efficient planing and hull control.

Different props may help but I think the other three issues should be dialed in first. Good luck, and keep us posted.

Re: Transom Bracket - twin outboards
 

Gillie said:
That 1.5" inches where Seacrafts do so well is for transom mounted motors. For every foot of bracket, add 1 inch to the 1.5" above the hull starting point. So for a 30" setback bracket, your starting point would be having the bottom of the cavitation plate 3.5" above the hull.

Re: Transom Bracket - twin outboards
 

What I found is boats with flatter deadrises are closer to 2" per foot of setback, and boats with deeper deadrises are closer to 3", but it really comes down to having someone driving, and someone looking at the cavitation plate when your running.

I moved my motor up and down 4 times before I finally was statisfied. As stated above, get the straight edge, and I would start with the cavitation plate 3.5" above the straightedge. With twin 4 strokes on the back, it is problably going to ride a little lower in the stern.

Then dial in the negative trim with the engine trim.

Re: Transom Bracket - twin outboards
 

open to all suggestions but the motors actually got a little better with the addition of the foils. however, they are easy to put on and take off; these newer ones do not require drilling holes in your motor - just have to loosen one bolt and they are gone.
the motors are supposed to go up two holes today and hopefully I can get it out to see what that does tomorrow.
will post when I have something new.

I REALLY do appreciate all the ideas!

Re: Transom Bracket - twin outboards
 

when you move thim put thim all the way up, I dont think with where your bracket is mounted you can get thim high enough and keep the hydrofoils for my 150's with thim
on I can cruse at 3100 when rough without 4100 is the slowest they are made to run on top or above water
not below

Re: Transom Bracket - twin outboards
 

I think you're right, John. Mine is at 3.5" with 30" setback.
http://i188.photobucket.com/albums/z...os/Cvpltht.jpg
http://i188.photobucket.com/albums/z...plthtclsup.jpg
It handles great but could probably go a little higher because cavitation plate is still slightly under water at typical cruise conditions. Motor is already at max height however, so I'd have to redrill the mount holes to go higher. Don't know how much higher I could drill the holes on this bracket.

Re: Transom Bracket - twin outboards
 

mine is set at 5 inches now the 250's were set at 7
bigger gearcase also required scoops for cooling
http://i833.photobucket.com/albums/z...erework001.jpg

Re: Transom Bracket - twin outboards
 

With the nearly 1000 lbs of motors hanging 2+ feet back you may very well need the SE foils. They certainly have benefits. I meant to edit that... Good luck, it looks like you're on your way.

Re: Transom Bracket - twin outboards
 

Denny, your 3.5 inches of height at 30 inches of setback fits the profile of having 1 to 1.5 inches above the keel when mounted at the transom, plus 1 inch additional height for each 1 foot of setback. (30 inch bracket = 2.5 feet of setback) And that's just the starting point for adjusting the motor height.

Re: Transom Bracket - twin outboards
 

what are you guys running for props? seems to be predominantly 4 blade props. The guy from the Yamaha parts (Andy) on The Hull Truth - told me that the prop I am running - the Yamaha "Reliance" 19 has a history of poor performance on many different applications.

Re: Transom Bracket - twin outboards
 

My most recent addition is a Solas 19p 4 blade. I should have gotten the 17P though for all around. I have a 3 blade 17 and 19. The 17 allows more rpm at lower speed (rough water, slower ocean speeds) 19P offers a little lower rpm but faster (cruising/waterway speed)

Re: Transom Bracket - twin outboards
 

I have tried lots of props I like the mirage plus sets
best but my starbord motor has a 135 ecu right now so it won't turn my 21 mirage plus so thats why the 4 blade
power techs after I get another 150 ecu if it still won't
swing the 21's i'll get a set of 19 mirages power techs
are 19's

Re: Transom Bracket - twin outboards
 

Denny do you keep yours on the trim pad? I see the
tiedown.

Re: Transom Bracket - twin outboards
 

neutral trim, the motors are in the second hole from the top - I used a straight edge and a level from the bottom of the hull, right under the drain plug....I measured to the cav plate just like in Bushwackers picture. 8.5 inches is what I get......my straight edge runs just about down the centerline of the lower unit - right thru the center of the prop.

Each hole only gets me one inch. I have one up and two down to work with- any ideas - now that you know what I have?

Sounds like I have a mess :(

Re: Transom Bracket - twin outboards
 

best option is to run it and see where cav plates are in the water ajust until they are above water then try some different props if geting water level set right doesent
fix it

Re: Transom Bracket - twin outboards
 

I'm running a 15x15 4B PowerTech. Blades supposedly have the old OMC SST profile. I ran an SST on my old 115 and it was an excellent prop. Not sure it's the optimum prop because it's about 0.5 mpg worse than my 14x20 Michigan Apollo 4B, but it seems to have decent stern lift, turns about 5450 with max load, gives me an awesome hole shot, gets on plane at only about 40% throttle, and lets me plane at about 12 mph with a very heavy load, which is nice in rough water. The Apollo seems to have even more stern lift even though it's supposedly a bow-lifting prop. Would like to try a 4B Apollo with less pitch or a BRP Cyclone 4B to see if I could still turn max rpm at max load but get a little better mpg.

Re: Transom Bracket - twin outboards
 

Good catch Duane! But that's just a helical screw anchor hurricane tie-down, not the buried telephone pole that an M-37 trailer requires! :D Denny

Re: Transom Bracket - twin outboards
 

Lobo1,
At the risk of being redundant here is a clarification with your picture altered.
My apologies if I got the wrong impression, but if you measured the height of your cavitation plates relative to the height of the bottom of your keel, you need to revisit that - I believe the base of measurement (where the straight edge lies)needs to be where the hull and transom meet directly fore of each motor.

Bushwacker's measurement is taken at the keel because that is where the engine is inline with the bottom of the hull (because he's running a single)

For twins set up the strait edge needs to rest on the bottom of the hull approximately where the white squares are in the picture.

http://i261.photobucket.com/albums/i...es/lobos23.jpg :rolleyes:

Re: Transom Bracket - twin outboards
 

OK. I will re-measure. My number was so far off from the 3-1/2" you guys were talking about.....I feel kind of stupid - having measured to the wrong spot but at the same time feel a bit relieved. At least I can get somewhere in the ballpark measuring where you are suggesting. Will go back tonight after work for a do-over.

Thanks again

Re: Transom Bracket - twin outboards
 

Setting these up is trial and error, but I think your going to wind up at 3.5" plus or minus an inch. It also greatly impacts the performance of the boat, and the fuel economy so it is worth the time to get it right. Another symptom of the motor being mounted too low, or the trim being negative is the wheel is a little harder to turn. Maybe it is just my boat, but that is what I found.