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Author Topic:   Props for a 27
Lewis posted 10-23-2002 10:17 AM ET (US)   Profile for Lewis   Send Email to Lewis  
I sold my 1985 OMC seadrives for $2500, I feel lucky. Delivery of my 2001 250 Yamahas came yesterday. I am going to photograph and post the repower process which includes installing an Armstrong bracket. I need props for the new engines. What size and pitch will give me the most efficient cruise speed? Thanks, Lewis
lhg posted 10-23-2002 02:35 PM ET (US)     Profile for lhg    
Lewis - STRONGLY recommend you purchase twin 30" shaft CR engines for a full transom 27. Additional cost is minimum on engines, and none on bracket. This will get the engines up nice and high. Standard twin 25" engines are a bit low on a 27.
lhg posted 10-23-2002 02:41 PM ET (US)     Profile for lhg    
I should have said 25" twin engines are low on a 27 when they are set back 30" on a bracket. They will tend to get swamped easier. Almost all of the larger, beamier boats are now designed for 30" shaft length twins, particularly when setback transom brackets are involved. When the 27 was designed, 30" engines were not available. Don't get talked out of this.
Lewis posted 10-23-2002 03:12 PM ET (US)     Profile for Lewis  Send Email to Lewis     
Thanks for the insight, but it is too late unless I sell these engines and start over. One thing I am courious about is the distance I can mount these egines apart. The wider, the higher, right? I noticed the ads for the new 31 Mako show the twins mounted much farther apart than you see on some boats. Any thoughts?
lhg posted 10-23-2002 04:14 PM ET (US)     Profile for lhg    
Can your dealer add the 5" extension kits.

On my Armstrong bracket, on my 25 Outrage, the 25" shaft engines are mounted on 27" centerlines. I think for the 27, BW uses 28". This will better accomodate the 76 degree V's of the Yamaha blocks. You might use the same centerlines used for the Sea Drives.

Capt_Tidy posted 10-23-2002 06:29 PM ET (US)     Profile for Capt_Tidy  Send Email to Capt_Tidy     
TO help with engine height... can a jackplate be added to a Armstrong?
Lewis posted 10-23-2002 06:47 PM ET (US)     Profile for Lewis  Send Email to Lewis     
You have more experience at this than I, why would the degree of the block come into play when determining the engine positions?
lhg posted 10-23-2002 06:52 PM ET (US)     Profile for lhg    
Yes, I think it can, and that is a situation I have considered also, for my next installation.

I think the key is to determine how much setback is desired, and the setback of the lift jack you plan to use. Then have the bracket made with a setback, minus the setback of the bracket.

Until the taller 225 HP engines came out, most brackets were done with a 26" setback. This is what I have for my 200 EFI Mercs, and in full tilt-up, there is no interference with the full transom. So if I were going to use a 6" setback transom jack on the bracket, I would order the Armstrong transom bracket made with a 20" setback.

Lewis posted 10-23-2002 07:39 PM ET (US)     Profile for Lewis  Send Email to Lewis     
The jackplate seems like a considerable additional expense. Do you think that the addition 30" setback will cause me to bury the new engines more so than the seadrives? And by mounting the engines, say 36" instead of 28" do you think that will give me the additional rise to prevent dunking. Also, I would think the wider I mount them the better the boat should handle around the dock. Is there a downside to mounting the engines father apart?
lhg posted 10-23-2002 08:31 PM ET (US)     Profile for lhg    
I think some posts sneaked in a little out of order. The wider degree V means the engines are wider than my 60 degree Mercs, hence the wider engine spacing makes them more serviceable. The OMC and Yamaha big block engines are wider than the 60 degree Mercs.

For a while, Armstrong was advertizing a wide spaced bracket, supposedly for better manueverability. You might want to call them for info. This would appear to get the engines up higher, because of the hull V. You might want to consider it, but I have never seen a 27 rigged this way. A special tie bar will be required. I kind of like the idea.

In the Reference section on transom brackets, there is a photo of a bracketed 27, with twin 25" OMC 225's on it. You can see the engines sit a little low relative to the boat.

It's a real shame someone didn't advise you to get 30" engines ahead of time, for a boat that large. But I am sure the 25" engines will work just fine. The cowls on the modern engines are pretty water tight anyway.

If you plan to do any downrigger or other fishing from the stern of the boat, don't get the full with transom bracket and side platforms. these get in the way of landing a fish, or using downriggers. Have the bracket made only wide enough to carry the engines, at the spacing you chose. The bracket probably won't be wider than the raised section of the transom. See photos of mine in the Rendezvous section.

Also recommend Sea Star II helm, and twin hydraulic cylinders.

lhg posted 10-23-2002 08:37 PM ET (US)     Profile for lhg    
PS You originally asked about props. I would recommend the Mercury 4 bladed "Offshore Performance" series. These can be purchased with interchangeable hub to fit Yamaha engines. Their stated design purpose is for "big Offshore twin engine rigs, requiring lots of hull lift and great holding". This sounds about right for a 27.
Yamaha may have now come out with their own version of this Mercury propeller, but it will proably coast more. The Merc Offshore's are about $400 each.
Lewis posted 10-24-2002 08:33 AM ET (US)     Profile for Lewis  Send Email to Lewis     
Thanks, good advise. One more question, I had planned on keeping the existing streering system. I think it was made by OMC, it is in excellent condition and was original equipment. I know I will need to extend the lines, but any reason not to keep it?
thebone12 posted 10-24-2002 12:07 PM ET (US)     Profile for thebone12  Send Email to thebone12     
The steering should be fine, but after I repowered my big boat, the steering went because of the torque of the new engines, it could go at anytime with those monster 250s. I would also go with mercury propls the mirgages 3 bladers. Also you have a blank sheet to work with on the transom, I would mount the engine as far a part as possible! More manuverability and also you can mount them higher so you dont have to woory about the shaft lenght, congrads on your new purchase.
Capt_Tidy posted 10-24-2002 12:38 PM ET (US)     Profile for Capt_Tidy  Send Email to Capt_Tidy     
Not to state the obvious but...

a hydraulic jackplate on an Armstrong would be the ultimate setup... a little $$$ but it would be wonderful to trim up and down as well as angle... and fun to play with.

Combining a shorter setback (i.e. cheaper) with a short jackplate or hydraulic jack plate (ie. cheaper) as suggested by Senior Goltz is a wonderful idea... two cheaper unti adding to slightly more money?

Q.. does the full width platform really get in the way for fishing... I would have thought it would be nice to have wide platform for standign and fishing.. downriggers are different I guess but mine are mounted at the rear anyway and wouldn't be hinded by a platform?

lhg posted 10-24-2002 02:10 PM ET (US)     Profile for lhg    
With the full transom 25, I think the full width bracket platform hinders fishability.
To stand on the bracket means climbing over the full transom deck, where there is basically nothing to hang on to. Offshore, in a 3 or 4' sea, this is an invitation to fall overboard, not a good idea with lines and downrigger wires out. I always work my lines, and two rear facing downriggers with 2' booms, from inside the boat. Incidentally, the top surface of the bracket, when at sea trolling, has water continuously washing over it. It is not dry, nor an advisable safe place to stand. That is why I recommend ordering the bracket to match the raised surface on the transom. However, if diving or swimming are the priority, not fishing, the full width platform could be an asset.

I would also emphasize that to use an Armstrong, or other, bracket, you don't need a full transom. They make a beautiful, and functional installation on a notched transom boat also. The splashwell drains need to be plugged or eliminated, and a bilge pump installed in their place.

thebone12 posted 10-24-2002 02:27 PM ET (US)     Profile for thebone12  Send Email to thebone12     
Stay away from jack plates. WIth a 500 pound motor on it, in 6ft seas I would not be comfortable, the jackplate will hold but the 3 foot bracket lever plus the jack plate with put a hurten on your transom in big seas.

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