Blue Jacket

[capt jake]

I have been on Tom's boat and simply loved it. the wife was beaming from ear to ear (and she WILL NOT go out on my sail boat).

I just created that album of the photos I took; I hope the link works, as I have a hard time with Imagestation lately.

http://www.imagestation.com/album/?id=4286656413&congratulation_page=Y

[tdrown]

Look's great, hope you have a fun time.

[capt jake]

As soon as my wallet will allow.........

Thanks!

[Frank Hagan]

You are a very mean person, Capt Jake!

Here's the plan ... I build the Spindrift to get my sailing fix, then the Blue Jacket because I know my wife will go in it. THEN, I'll build the Princess 22 after my wife has gotten over the ordeal of me building the Blue Jacket. Or maybe not.

You are a very mean person!

[Frank Hagan]

Ah, you're probably right!

Time is my problem, though. I had thought as the kids get older, with one moved out and the other on her way to being a responsible adult, that time would be a bit easier to come by. Fat chance!

Seeing the pics of the recently launched Spindrift has encouraged me again ... I really want to get it built to have something to launch in ten minutes and single hand around the harbor.

[capt jake]

Time is my problem, though. I had thought as the kids get older, with one moved out and the other on her way to being a responsible adult, that time would be a bit easier to come by. Fat chance!

I hear ya there; time is hard to come by for me lately also.

You are a very mean person, Capt Jake!

You think that's mean? How do you think I feel? Now I have easy access to pictures to remind me! :shock:

Just trying to convince the CFO here that we really really 'need' this! ;)

[capt jake]

See more from the designer at

http://media5.hypernet.com/ubb/ultimatebb.php?ubb=get_topic;f=2;t=003503

[Brent]

Jake and others,

Thanks for the postings about these boats. I have been investigating the Blue Jacket as a possible project, and was delighted to find the pictures and discussion.

I have the study plans, and the pictures helped to address a few more of the subtleties.

I am not to worried about the deadrise issue. There is plent of deadrise in the Blue Jacket to take on the type of water I am likely to encounter. I'll leave the deep V for the serious offshore boats.

[capt jake]

Great Brent!! I loved the boat when I got the chance to go out on her!!!

Now for the $$$........ Not a really expensive craft, but the $ re still there.

[Brent]

Would anyone care to speculate about the impact of increasing the mounted horsepower on a boat like the Blue Jacket?

The 50 HP in the plans sounds perfect for cruising; the intended purspose of this design I understand. My kids talk water skiing! Which of course takes a few more HPs.

All it takes is money to buy a larger motor :wink: , but then the thing has to be mounted on the boat. The larger motor will weigh more, and therefore change the trim of the boat. Fuel consumption will no doubt be more when pulling skiers, but may/maynot be different when cruising? I suppose the transom strength might need to be looked at. I have only the study plan which doesn't go into detail here, so I really dont know how the present design is set up, or if any change would be needed. Would love to hear some opinions.

I almost hate to go tweaking this design, as this boat has high asthetics as designed. But...

[Frank Hagan]

Tom only lists the 50hp in the plans. It plans easily at 23mph with the 50hp; I guess there's no reason you couldn't put more power on the stern. In the plans, Tom mentions that the weight distribution of the Blue Jacket is further forward than most 24' boats, so trailer selection is critical. Judging from the pictures here on messing-about of Liz at 8, 16 and 23mph, even with that "weight forward" issue, I think you are right that you would have to balance out the trim of the boat. She might be too "bow up" with more weight on the stern.

Over 20 plan sets were sold as of my last correspondence with Tom, but I don't know of any that have been built yet. Tom pops in from time to time, so perhaps he'll join in and give his opinion of extra weight or power on his design.

[capt jake]

Tom has embraced the 60hp version of the motor he put on; but no more!

Basically, "If you want a speed boat.....!" 50 or 60 is plenty on this design, it realy isn't engineered for teh added stresses and weight of naything larger. And as Frank pointed out!

[capt jake]

She might be too "bow up" with more weight on the stern.

That is one of the things I really liked when on his boat. It didn't push the bow up when getting to a plane; it stayed relatively level. Better control and visibility.

[Tom Lathrop]

Thanks for ringing my bell Frank.

The issue of adding power to the Bluejacket comes fairly often but this is the first time anyone has specifically wanted to pull waterskiers. It was a very simple answer to use the 60hp Yamaha because it is just a souped up version of the 50.

First, a couple of clarifications. Using an engine of 90hp will give no problem with trim or weight. I often operate with two adults sitting in the seats on either side of the engine and that is a lot more stern weight than the extra 130lbs of the larger engine. How much faster will the boat be? I'd expect speed in the low thirties.

If the speed of the 50 or 60hp engine is fast enough, there is ample power to pull the skiers. Heck, I learned to ski behind a 10hp outboard. Most people will want more speed for skiing though.

What are the issues?

Weight -- Not a problem.

Size -- May require some rearrangement / design of the stern area. The 50/60 just fits in the space allowed and gives room for the nice permanent seats. A wider engine will require narrowing or possible elimination of these very useful features or, perhaps reduction of the ttumblehome in the stern topsides. Use of a 2 stroke engine may make this problem moot, since their powerheads are quite a bit smaller than the 4 strokes. I

[Brent]

Tom, Thanks for the reply. This is exactly the analysis I was wanting.

[Guest]

AAAAAAAAHHHHHHHH, have you ever given some thought of increasing the angle of the stern, for the heavier Motor? Have you given any other thought on prop changes, if you will be using the boat for waterskiing? Top end will come into play with some cuping of the wheel tips. This can be done with the same hp engines. It may take a little work for some weight shifts????????????? You will need to be somewhat conservative with running topend, as it may generate some additional heat. Trim tabs could do wonders, in this case, too, when adding the extra weight. Nope, I am not changing this boat, just thinking out loud for some individual needs, Tom??

[Brent]

Motor boats is something I have much less experience with tweaking. But my engineer trained brain is beginning to process the possibilities.

I fathom how changing props might trade higher top end for slower speed economy. Cant have it all now can we! Would it be appropriate to think in terms like to pull a skier one needs speeds in the high 20s to mid 30s and enough horses to get the skier up and out of the water? There would be some X amount of HP needed to do this, a function of amoung other things the boat weight/length, plus the resistance of one average skier. Once the HP is figured out, the prop could be tweaked to optimize performance. Am I close here?

[Tom Lathrop]

One thing to remember about outboards is that they have only one gear ratio. If you use a too low pitch prop for low end acceleration, the engine will overspeed at WOT. Think of running your car in second gear at WOT.

Using a too high pitch prop will be like taking off and running up hill in too high a gear. The engine will always be under stress. Manufacturers give a desirable RPM range for WOT. The prop pitch should be selected to put RPM in the range they give. This will vary with each boat. Cupping is a way to load a too low pitch prop to make it load like a higher pitch to the engine. Even a very small amount of cup (hardly noticeable) will drop RPM like about two inches of pitch increase will.

Few people select props properly but everyone should. Like everything else in boat operation and design, it's a compromise.

Not sure I understand what Mike means by changing the transom angle. The only adantage in putting trim tabs on Bluejacket would be to correct for lateral trim angle due to too much weight on one side. Easier to get the passengers to not congregate on one side. Otherwise, trim tabs are not needed and I would not consider them at all. The boat has high longitudinal stability as it is.

[Guest]

Tom, as stated in the past, some of my posts do not translate well from brain to words. :wink: So with few words, in my own way, :wink: may work for me and clearing up your questions.

We have in the past improved trim and planing with additional wedges between the motor and the transom, allowing the motor to tuck under and give a new shoving angle when we have needed to push the bow down. This also has been done with wedges across hull bottom , on each side of the motor well, on the actual planing surface of the bottom, done in 1/4 increments till happy with it, when additional deadweight, is added on the transom.

Many of the engine manufacturers now make aluminum ones or we place a wooden one, fabricated by plywood and glass, again depending on the thickness of the sterns, because ot the normal motor bracket size of around three inches, that allow for the engine to trim further "under" or the propeller angle is greater to the planing surface of the water. So when you have, for example an 11 degrees stern for many vee hulls, you will then have say 13 or 14 degrees now. The old theory was that you can always trim a motor back up, but you can never the bow down without any mechanical means,if your angle or horsepower is too little for the exisitng hull.

Sometimes when we update the interior layout, this becomes necessary too say a cabin is added or removed. Most fiberglass boats become heavier with age, too, causing the need for more angle too. This was and is my thoughts on a larger motor, additional weight, when a boat, so finely trimmed and minimun hp is used.

One reason for this has been the need or desire to place a larger outboard, adding addditional weight to a boat originally designed for a smaller engine.This was the case in many of the older engines, many two strokes especially, since an increase in hp caused a need for more actual cylinders, creating more weight of the engine.

It is a point of note, that many updates in hp for the four strokes are done by carbaration, and not in additional cyclinders now. The materials of the blocks and more plastic parts cause less additional weight changes in engines now, too.

Few people do a lot or worry about refining the props on outboard motors, since weather and load causes performance to change at a greater rate than a conventional inboard power boat. If the outboard runs on plane, and the top end RPM is close to specs, upon shelter or calm water seatrials, thats as much as is addressed to this issue. The cupping can do wonders for the waterskiing issue, but a close association and working relationship between a good motor dealer and local prop shop is essential when doing this and highly suggested before modifying the actual angle of the sterm.

The wedges would be where[in my honest and opinionated opinion] I would start, between the motor and stern, and maybe use it.

Please accept my words as just them, Tom, and no attempt to insult you and your fine work on this hull.. This has been dealt with in many of one off boats under thirty feet, and old style glass boats such as the many redoes on the Sea Crafts and Makos.

[Tom Lathrop]

Mike,

First, that is what I thought you might mean and it is now very clear. Second, I'm not in any way insulted when anyone questions anything. and I know that you have been working at the grass roots (or water level of small powerboats) more than I have.

Wedges, motor bracket and hull -- I set the transom angle at the normal 11 degrees and that seems to be just fine at normal operating speed at all water and load conditions. Several things are at work here. First, there is the forward location of the CB relative to many other pwerboats. Second, there is the chine flats design which are set to a down (positive) angle of one degree relative to the hull bottom. this means that the width of the flats gradually increase toward the stern. The forward CB tends to hold the bow down and eliminates porpoising. The flats give extra lift to the stern without the drag of trim tabs and contribute to the level running attitude.

Bluejacket has more than the normal longitudinal stability. Changing the motor trim angle has very little effect on boat trim. If I eliminated the chine flats, both hull trim angle and top speed would increase at the expense of low end planing and level running attitude. I sacrifice top end efficiency for low end efficiency. The big manufacturers could never sell many boats with that claim but then, I ain't trying to compete with anyone.

Cheers, Tom