Devlin BB3

[font=Verdana,Arial,Helvetica][font=Verdana,Arial,Helvetica]In my experience, with the motor trimmed the bow will pop up when you are taking off.[/font][/font]
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Agreed, motor trimmed down ( not all the way) till up on plane.

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When you plane off, trimming the motor up will usually suck the bow down even more.
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This does not sound right.

Once up on plane, trimming the motor up should on two things.
(A) the bow will begin to lift. If you prop has enough "cup" the bow will lift to the point of porposing.
(B) the engine RPM will increase due to less water resistance as the bow rises. This will continue untill either the prop "blows out" or the bow is wildly porposing.
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I have a 17.5' run-a-bout (bow rider) that does the same thing. Once on plane, when I trim up a some and get an extra 5-8 mph out of it, the bow definetiy comes down a little more. There seems to be a sweet spot there. This boat did that too. I did get some proposing with it and put the trim tabs down a little and that took that right out.
 
I was surprised to see the trim tabs. Generally you only need them if your having a porposing problem. I would try running without them. The RPM issue sounds like the wrong prop. You should top out at about 6k. If you can't figure it out go over to the refuge and pose the situation to USA-1 he will be your best bet to a solution. He is a former boat racer and has done testing for Mercury and now Tohatsu. He just stepped down as a moderator but I believe he is still active on the site. Good luck.

Tom
 
Thanks for the info Tom. Tomorrow I'll call the tohatsu rep I've been dealing with and run it by him. We started off in the middle with a 12 pitch prop. I'll have to play around with it to see what's going on.
 
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Once up on plane, trimming the motor up should on two things.
(A) the bow will begin to lift. If you prop has enough "cup" the bow will lift to the point of porposing.
(B) the engine RPM will increase due to less water resistance as the bow rises. This will continue untill either the prop "blows out" or the bow is wildly porposing.
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Yes on all this.
 
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Thanks for the info Tom. Tomorrow I'll call the tohatsu rep I've been dealing with and run it by him. We started off in the middle with a 12 pitch prop. I'll have to play around with it to see what's going on.
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I don't think you need to go there yet. I would set the motor with a straight edge at "O" trim, meaning cav plate inline with hull bottom. Set tabs to "O" as well and see what you get for rpms and speed.

The BB3 is the least finicky of the Devlin hulls and people seldom have issues with them as far as getting them dialed in. I'm sure you will get this licked asap. Get the right prop on there and maybe raise it up and you will be flying.

The Devlin hulls have a lot of bow rise at low and mid rpms and take a lot of power getting on plane. The high bow is an attribute in heavy seas (your tabs are probably eliminating some of what a lot of us consider a positive thing with the high bow at moderate throttle). The BB3, I believe, has less bow rise than some of the other Devlin designs.
 
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Thanks Tod,
I'll have to check it with a straight edge. The manual calls for 0.4" - 1.2" below the anti cav plate. And are lower end of that range. I have run it trimmed all the way down and tabs all the way up. I get plenty of bow rise if I trim the motor up a little and slow down. I have to admit, it's a little unnerving when the bow goes up and the stern squats down in the water. At lower (1500-2000rpm) speed it doesn't take much trim to do that. I'm not used to it yet and have not really pushed it hard...not in cold water.
 
You did a fantastic job on that boat! Always good to see another BB3 in service, you will get a lot of good use out of her once you get things dialed in.
 
Thanks Cody,
When I was trying to decide which boat to build, the pictures of yours helped. Now I have to get used to sitting this low in the water. Oh - look at the Feelfree gravity kayak seat. I bought 2 of these and they are a perfect seat solution for these boats. Not cheap but works really well.
 
Thanks Tod,
I'll have to check it with a straight edge. The manual calls for 0.4" - 1.2" below the anti cav plate. And are lower end of that range. I have run it trimmed all the way down and tabs all the way up. I get plenty of bow rise if I trim the motor up a little and slow down. I have to admit, it's a little unnerving when the bow goes up and the stern squats down in the water. At lower (1500-2000rpm) speed it doesn't take much trim to do that. I'm not used to it yet and have not really pushed it hard...not in cold water.
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On the motor height, the manuals are usually conservative and performance is usually better slightly lower, but for sure that is a minor issue in your inability to reach 30+ knots in that boat. My snowgoose, which is a much larger boat in every dimension does 30 knots with a light load with my Yamaha F40.

Trust me - you will like the high bow on the first day you are out and the wind picks up and the waves stand up high against the tidal flow.
 
Devlin bb3 ? - do most of these need trim tabs to plane right and handle?
John
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I put the trim tabs on not so much out of need but more out want. Sam recommends a 25hp motor for this boat. It use to be 30hp. After searching this site and talking to other people who have built the boat, the concensus was that 25 is not enough.

So I researched 30 and 40hp motors. I also went to the coast guard tables to varify if a 40 was even acceptable. It is.

So now with the 40 that's a jump in block size and weight. It weights about 215. I put the tabs on to give me more planing surface, the ability to fix any porpoising that may occur, and to be able to balance the boat if I end up loaded heavier on one side.
 
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