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Dialing in 27 Seacraft engine height, etc.

Old 01-11-2021, 10:14 AM
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Default Dialing in 27 Seacraft engine height, etc.

I have a 27' Seacraft with new 48 inch wide body Armstrong bracket with 30 inches of setback and 14 degree transom angle. Engines are twin Honda 250s with 30 inch shafts. Boat jumps on plane and runs very flat at 51mph at 6300 rpms WOT with 15.25x17 three blade Solas props. Engines are mounted in hole number three of five. When using a straight edge coming off of hull (measured directly below motor) the cavitation plate is roughly 4 inches above hull. No trim tabs yet.

While speed is fun, rough water performance is what I care about the most - I boat in the North Atlantic and the water is always rough. When running in chop at cruise (27mph or so) at the current engine height, you can hear some prop ventilation. Motors are normally trimmed all the way in (negative) and when I trim them out one click at higher speeds, the response is okay but not great. However, if I trim them out two or three clicks, boat will porpoise a bit.

In the interest of getting great rough water performance while maximizing fuel efficiency, I am thinking of lowering engines one hole and switching to four blade props because of their increased surface area. In doing so, I was hoping to minimize ventilation and maybe give myself some more positive trim, so I can run engines perpendicular to water surface at higher speeds where fuel efficiency is greatest.

Obviously the boat is running pretty darn good and I am splitting hairs here but if the experts have any suggestions or if I am missing anything and/or may have interpreted things wrong, I am all ears.




Old 01-11-2021, 10:26 AM
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Copy and paste to Classicseacraft.com, if you have not yet. That’s a very rare hull, but there are a few members there that can assist.

Zotcha.
Old 01-11-2021, 01:41 PM
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Before I was done reading what you wrote I was thinking drop two holes and go 4 blade. I bet the added stern lift will be beneficial but it will also raise the stern so I bet you have to go down two holes. On my 21 Contender I had a Yamaha sws 2 prop with the engine as high as it could go and I felt like it could go higher. I changed to a Rev4 and it would ventilate so I had to go down a hole. The boat's attitude was much improved though with the Rev4. The change was miraculous.
Old 01-11-2021, 01:49 PM
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Originally Posted by jbg108 View Post
Before I was done reading what you wrote I was thinking drop two holes and go 4 blade. I bet the added stern lift will be beneficial but it will also raise the stern so I bet you have to go down two holes. On my 21 Contender I had a Yamaha sws 2 prop with the engine as high as it could go and I felt like it could go higher. I changed to a Rev4 and it would ventilate so I had to go down a hole. The boat's attitude was much improved though with the Rev4. The change was miraculous.
this...... Rev4s are amazing screws. Many people truly don’t understand how big a difference a boats propellor(s) can make. I would try the 17”s. You may drop back to around 5800-6000 in rpm, but your “issues” will vanish. They have a lot of stern lift so that should eliminate the porpoising, and they love to run high and have tremendous bite, hard to blow them out. Confirm this theory with Ken at propgods, but I think this would be the starting point he recommends.
Old 01-11-2021, 10:52 PM
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Your on the right track. Lowering one hole and going four blade will do what you want.
Old 01-12-2021, 04:05 PM
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nice hull. i have a 1977 23' Seacraft, Armstrong bracket, single verado 275. run Rev4 17P and its a great prop. stern lift is excellent. i can run wot throttle full loaded and be about 6000rpm in flat water trimmed up. results vary with loads etc. i can approach wot red line with light load on a flat day inshore Wellfleet. my red line is 6400RPM. you want to be near red line wot trimmed up. engines like some speed runs . no cavitation in a Miami vice turn in little pleasant bay around cans with the rev 4 which the 3 blade mirage plus did have. have a mirage plus (forget pitch maybe 19 maybe 17) sitting gathering dust. it went 2 mph faster in wot. cavitated on turns. far as plane speed the rev4 is lower vs mirage= better on rough seas. i have trim tabs. helps immensely. I would not run an ob bracketed boat without them. huge huge difference.

so another vote for Rev4. that said, never tested anything else....stern lift time, lower planing speed, never cavitates. Rev 4 for the win for me.

edit-the mirage plus is indeed17P but was running a verado 250hp. when went to the rev 4 17P I also 'upgraded' the same verado to a 275hp. so not quite an apple to apple comparison on pitch and time to plane as changed variable by 25hp. i never raised the Verado height with the rev 4 but sure is tempting. i actually forgot about raising it 1 hole with the rev4. maybe someday this year will do.

Last edited by josh_wellfleet; 01-12-2021 at 04:10 PM.
Old 01-12-2021, 09:06 PM
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I have a 25’ Seacraft with rev 4’a and really like the way they carry the boat. Obviously different hulls, but the props work well.

I would like to see pictures of your boat if you have any. What year did Seacraft make a 27?
Old 01-12-2021, 09:32 PM
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Before you move engine height, try 17 pitch Enertia Ecos and 17 pitch Rev 4s.

I suspect one will be the answer without dropping the engines down a hole.
Old 01-13-2021, 06:57 PM
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Originally Posted by cp5899 View Post
I have a 25’ Seacraft with rev 4’a and really like the way they carry the boat. Obviously different hulls, but the props work well.

I would like to see pictures of your boat if you have any. What year did Seacraft make a 27?
Thank you all for the feedback. I will try and track down some Rev 4s. Attached are some pictures. Seacraft made some flybridge 27s starting in the late 60s and into the 70s. In the mid 1980s...they made approximately 10 of these 27' Tournament models and some center consoles too. Mine is a 1986 model that I bought from the original owner who was 79 when he sold it to me in 2014.




Last edited by Trydent; 01-13-2021 at 07:04 PM.
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