I/O weight for Double Eagle angle True Grit

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ClayKorn
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I/O weight for Double Eagle angle True Grit

Post by ClayKorn » Tue Feb 24, 2015 8:23 pm

Hi all,
So in researching boat plans, I noticed that both True Grit and Double Eagle have weight limits of 600 lbs for sterndrive configurations. However the Olimpian 23 has a limit of 1200 lbs. When looking up the specs for the engine and sterndrive, even the Mercruiser 3.0L comes in at almost 800 lbs. When I searched this forum, I found conflicting answers regarding these weight limits.

What are the factors that drive this limit; transom width, volume in the aft sections, stability, balance, etc?

If these limits are exceeded (several examples of Double Eagle are built with I/O's), what are the repercussions?

I'm interested in a boat that will perform well at both mid-range and slow speeds. I'm concerned that the Olimpian would not perform well at slow speeds as it is a deep vee hull.

Clay

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kens
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Re: I/O weight for Double Eagle angle True Grit

Post by kens » Wed Feb 25, 2015 1:52 pm

I have inboard version of Double Eagle, and can attest that it performs well at mid range and low speeds.
Yes, some examples have exceeded the weight of I/O per the plans. I dont know the specifics of those, but they seem to do OK.
Oak is over rated, everything about it takes extra time; then it warps, splits or checks !!! :roll:

dmac
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Re: I/O weight for Double Eagle angle True Grit

Post by dmac » Wed Feb 25, 2015 3:23 pm

Is it possible that a 10% hull extension would provide some extra buoyancy aft to help support the weight of a sterndrive power plant? Just a thought FWIW. Cheers and good luck.

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raymacke
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Re: I/O weight for Double Eagle angle True Grit

Post by raymacke » Wed Feb 25, 2015 7:26 pm

This post is long (I get carried away) and I am assuming you are looking at an I/O. If you are thinking about an I/B I think Kens is right and there probably would not be a lot of adverse performance for a little additional weight. That weight would be carried closer to the C/B and not tend to shift the hull out of trim as much.

Deep Vee designs potentially have more below the waterline volume at the transom which tends to allow them to carry more load. Shallower Vees on the other hand have less volume and are more sensitive to additional aft weight. But Deep Vees are designed to operate most efficiently on plane and do create more drag when going slow. As mentioned one possible solution is to lengthen the hull but with the True Grit/Coastal Cruiser going form 25' to 27' increases the allowable weight by 100# (600# to 700#). But still that is not enough to accommodate the 3.0L I/O and stay in trim.

Can't speak about the Double Eagles but I know there have been several builders that have installed the 3.0L engines in the TG/CC hull and are running them with no problem. BUT your question is will they run efficiently? I am no expert but my guess is it does indeed compromise somewhat the low speed performance. Here is a photo of Gary Stookeys very nice aluminum True Grit with a 3.0L installed The shot is on the trailer but note the waterline stain. (photo from Glen-Ls page on the TG)

Image

As per plan the waterline should actually be parallel to the chine along the aft 2/3s of the hull. On Gary's boat the waterline crosses the chine about were it should but obviously it is squatting and my guess is the transom is setting about 3" deeper than it should. Gary's situation is aggravated by also having the 115# 15 hp kicker mounted back there. I have to believe this configuration is hurting the low speed performance as the lower transom is digging a deeper hole as you move. High speed is probably effected too but not as much as more of the transom is being lifted out of the water. But this was a trade off Gary was aware of and willing to accept. I corresponded with him about it. I was concerned about the foot end of the berth ending up higher that the head end(aft) making it uncomfortable to sleep. Here is what Gary replied about the situation -

The stern is down with the weight. The only weight I could remove would be the outboard and that's 115#. But I had to use it to come home with 5 hours on the main eng. The starter solenoid went out. So its been very useful so far, I use it trolling all the time too. It burns very little fuel and is quiet. I was very impressed with the weight carrying ability. I have had 4 grown ups and a few kids aboard and it will still get up on a plane and run 20 mph. But sucking lots of fuel and making lots of noise. I would rather cruise at 10 mph where its quieter and smoother. It seems so slow to go 6 where its at hull speed and cheap to run. The out board will push it 5mph so you could run real cheap.

I also ran into a Coastal Cruiser (wood) with a 3.0L on Kentucky lake. Again I could see it was squatting. If I remember correctly the owner told me he usually cruised about 10 or 11 mph and was somewhat disappointed he was only getting 2 mpg (about 5 gph). Honestly that doesn't surprise me. His cruise speed is about my 60 hp TG's top speed. And even though I am lighter at the transom than him at 10 mph I really don't think it is planing - still plowing a lot of water. Here is a photo of the CC at cruise -

Image

Note the rolling wake behind. Just don't think it is planing and it is operating in a zone that probably produces the poorest fuel economy. My guess is it will take about 15 to 17 mph to make it plane cleanly. But then again this is a "semi-displacement" hull and honestly I don't think it will ever really plane efficiently. The hull design is a compromise that operates fairly well at slow speeds but CAN be pushed fast enough to plane. It will require more HP to plane (i.e. more fuel) than a planing hull but will operate more more efficiently at low speeds than the planing hull. Obviously it is a trade off.

My thought is the semi-displacement hull is ideal for the people that want to go slow (displacement speeds) the vast majority of the time but would like to have the ability to go faster if the need presented itself - like getting out of the way of an oncoming threat or weather. If you want to run more than 7 mph or so on a regular basis I personally would be looking more at the Double Eagle or similar. It is still a shallow V but a true planing design but will offer reasonable lower speed performance. Still aft loading it with an I/O will hurt the low speed end somewhat - there just isn't anyway around it.

BUT have you considered and O/B? For the Double Eagle a 115 hp Mercury 4 stroke at 363# is fairly close to the allotted 325# as per plan and should perform well at both slow and faster speeds. I realize it may not offer the "look" some builders are wanting but it does provide a very workable solution. I have been very pleased with my setup.

(OK, I know KENS just had a stroke! - A Double Eagle with and outboard - What? - BLASPHEMY!!!!!) :lol:
So Many Rivers,
So Little Time....

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kens
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Re: I/O weight for Double Eagle angle True Grit

Post by kens » Wed Feb 25, 2015 10:26 pm

dmac wrote:Is it possible that a 10% hull extension would provide some extra buoyancy aft to help support the weight of a sterndrive power plant? Just a thought FWIW. Cheers and good luck.
I did the 10% stretch, and yes, it adds buoyancy.
OK, think this way if you can follow my rambling.
Great many boats have trim tabs approx 8"x8" each side of the transom to lift the extra weight of 'transom warts' (outboard motors).
The math tells you that is 128 sq in of trim tab. They will lift the transom at speed but provide no buoyancy.

Now consider a stretch of the hull. Stretch a Double Eagle 10% and that is approx 18" length. FULL BEAM width. Say, 7 foot beam at transom and 18" long, how much area is there for lift at speed??? Plus it does add buoyancy. I have the stretch, and, no trim tabs, never need them, why bother? Yeah with the stretch you adjust componants for the new CB, but you still have the extra lift and buoyancy. The stretch is a win - win deal.

Are you going to use it in salt water? I once had a I/O in salt water and the corrosion issues were insidious and horrific. That was a big deciding factor in my inboard engine decision. Also, when you run the prop sizing programs on computer, an I/O takes a penalty versus the inboard for the same given boat. I am operating in salt water, mostly offshore, and turning in fuel economy numbers that have only been beat with a smaller boat, smaller engine, or, a displacement trawler.

I have run the math, and the math tells me I can make the Bahamas crossing on 18 gal fuel.
Can anybody else do that?
Oak is over rated, everything about it takes extra time; then it warps, splits or checks !!! :roll:

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kens
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Re: I/O weight for Double Eagle angle True Grit

Post by kens » Wed Feb 25, 2015 11:16 pm

raymacke wrote:
BUT have you considered and O/B? For the Double Eagle a 115 hp Mercury 4 stroke at 363# is fairly close to the allotted 325# as per plan and should perform well at both slow and faster speeds. I realize it may not offer the "look" some builders are wanting but it does provide a very workable solution. I have been very pleased with my setup.

(OK, I know KENS just had a stroke! - A Double Eagle with and outboard - What? - BLASPHEMY!!!!!) :lol:
BLASPHEMY!!!. for sure.... :lol:
But please hear me out. The bigger outboards are not as light as you may think. It is easy to read the sales brochures and think a big outboard is lightweight. But, those numbers are posted as dry weight, no prop, no controls, no anything, purely presented for the salesman' delight.
My cast iron inboard with a cast iron Velvet drive is 700#. A 2 stroke 150hp outboard is 'presented' @ 525# dry. Consider the outboard is all exotic aluminum alloy castings and plastic, I personally dont see that as a weight gain. Since my own engine was an Ebay compilation of parts, I am all cheap cast iron. IF, I had spent the money on aluminum parts I could shave off a full 100# for a 75 pound difference. Since the outboard cannot produce the torque of an inboard, I consider that a equal push. And here, I quoted a 2-stroke, if you look at 4-stroke outboard then the inboard well purchased probably has a clear advantage.

Ray is doing well with his outboard, probably because he purely wanted to enclose it in a sound deading box, and he is operating it at low power. He did his math and got his CB on spot, and runs well. BUT, he only needs about 10hp to do what his boat does best. Running a 60hp motor @ 10hp settings equates to a quiet operation. And quiet is what he wanted. If it works good and lasts a long time, then leave it alone.

AS far as blasphemy? I thought about a 115hp outboard with a manual tiller. A Double Eagle with no cabin, no skeg, purely flat, open, floorboards and a tiller outboard. I thought about it but didnt make the jump.

I went fishing in a modern fiberglass 19 foot boat with a 150hp outboard. I wasnt really impressed. I sat at the transom when we were leaving a fishing spot, I said "Get IT". He hammered the throttle, and I never saw nor heard the such as the commotions goings on. A tremendous hole in the water, the bow up in the air, the motor noise, and it all seemed to be struggling to get over the 'hump' and on plane. I was less than impressed. As a kid growing up on the banks of the Ohio river, I seen 45' steel hull get up on plane. This 'glass boat didnt impress me. I buiult a inboard.

The outboards and I/O's just cannot make the torque that a inboard does.
I do not know why. I have run the math and it seems to be a equal push. It just is a disparity that exists.
If I mount my 17x14 4blade wheel, I can go from idle to WOT in 2 boat lengths. If I mount a 15x15 I can make the Bahamas on 18 gallons. I dont know why.
Oak is over rated, everything about it takes extra time; then it warps, splits or checks !!! :roll:

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raymacke
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Re: I/O weight for Double Eagle angle True Grit

Post by raymacke » Thu Feb 26, 2015 7:41 pm

Hey Ken, I can beat your number! Would only take me a little over 8 gallons to do the 54 miles.

But then again while I am making the run you could go back and forth 3 times and still have to hang around the bar to wait on me to get there. :D Just BSn. I'm sure if you only ran 6 to 7 mph your mpg would be a good bit better than mine. At 6250# my guess is I am a lot heavier than you and no matter what engine setup you use weight incurs a performance cost.

Performance wise there are probably several advantages an I/B offer over either O/B or I/O. For one thing the power line is more or less straight. In other words, the crankshaft, drive shaft and prop are all running in a straight line or fairly close. An O/B the power actuall makes a 90 degree turn and in an I/O it make two 90s. I don't know exactly what the hp loss is but it has to be a fair amount. Next I/B often swing a larger diameter prop. If I remember correctly your HP is about 135 and you are turning a 17" prop. That range of outboards is probably going to have a 14" or 15" prop. Adding 2" of diameter is a lot and it allows you to operate at a lower prop rpm. And the large diameter and lower rpms always equals better efficiency.

But O/Bs do have advantages. Yes, there is a lot of aluminum and some plastic but most are rock solid dependable. I'll put my Hondas or a Yamaha up against any gasoline marine engine out there. And the four stroke O/Bs are reasonably quiet. If you live in colder climates there is no winterization which is nice when those 50 degree days pop up in January and you want to take a spin knowing next week it will be zero again. Installation is much easier and although I know kens will argue the point I think maintenance is easier too. I have never owned and I/B but have had several I/O. Love changing oil by feel and trying not to end up with a quart of used oil in the bilge. And speaking of bilge with an O/B you can have a totally dry bilge 100% of the time - no water in the hull just outside where it belongs. Many I/B have a problem doing this. No through the hull penetrations needed which can have hose failures and sink the boat. That's enough - everyone get where I am coming from.

Ken likes I/B - I like O/B. But that's why you build your own boat so you get what YOU want not what we want.

(BTW - kens and I are friends and we both like needling each other about this!!!!)
So Many Rivers,
So Little Time....

ClayKorn
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Re: I/O weight for Double Eagle angle True Grit

Post by ClayKorn » Thu Feb 26, 2015 9:15 pm

Thank you for your great responses.

I find myself stuck. Every time I'm ready to purchase a set of plans, some detail pops up that changes how I look at the different designs. I think it really comes down to wanting too much out of a boat. I want a boat that can comfortably cruise rivers, ICW and even trips to the Bahamas. And also, I want a boat that is also easy to trailer to the point of being able to drop it in the water for an impromptu evening cruise; a boat that would not only be enjoyable to me, but my whole family (wife and young child). Raymacke seems to have solved this problem with having two boats. The CS-20 for the ease of launching and funner speeds of planing. While the modified True Grit is used for the comfortable slow cruising. This may be the route I should take. Find a "for now" boat to use as a fun overnighter. Then later in life when I will have more time to actually spend weeks or more on a boat, get a larger more comfortable one.

I do believe that I want an inboard or I/O for the "for now" boat to minimize noise.

The Double Eagle looks like a great design. I do have reservations about the cabin headroom at 4'9". I would have to bend over quite a ways to get in to use the facilities / or get int the bunk.

The True Grit has a better cabin layout and headroom at 5'7". However, with it be 25' long and coming it at over 5000 lbs., it may be harder to trailer, launch, and retrieve than desired. I would want to build it at 23' rather than the 25'.

I will also look at some of the smaller boat that may fit what I can use as a "for now" boat.

Thanks again for the responses.
Clay

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Re: I/O weight for Double Eagle angle True Grit

Post by raymacke » Thu Feb 26, 2015 11:23 pm

some detail pops up that changes how I look at the different designs. I think it really comes down to wanting too much out of a boat.
That is a dilemma MANY of us have faced. Personally, I look at plans for two years. Among other things, I really wanted a flybridge with a full displacement hull. But I couldn't find those features on a boat that met the rest of my criteria. Had to make a list of what I wanted in the order of importance and then find a design that was close. That dirty word "compromise" is ever present when deciding on a boat project. And yes, I do have the best of both worlds with two boats serving different missions.

About the True Grit - if you are willing to accept operation "mainly" at lower speeds the TG is a very nice design. You mention going I/O or I/B because of noise but I am willing to bet my O/B setup is quieter than either. Two things contribute to this - first, mine is bracket mounted. As a result it is totally outside the hull. From the helm I can see just the top of the cowling and the transom blocks a great deal of engine noise. Second, at cruise I am only turning about 2700 to 3100 rpms (WOT 5500). Like kens said probably only using 10 to 15 hp of the 60 hp so the O/B is not working hard or creating much noise as a result. The engine could be transom mounted with a splashwell and a cover could be fabricated to reduce the sound - similar to my Cabin Skiff. Weight wise if on the transom a 60 would be a piece of cake and perhaps a 75/90 hp O/B would be workable. But if you are not interested in a O/B and thinking of the 23' version I would option for the I/B as I think the I/O would be a weight problem - just not enough hull to support it.

The TG will not be a light weight by any means but I do tow mine all over the place with a 1/2 ton Ford F150 2wd pickup. The total tow weight including boat, trailer, fuel, water and gear is probably about 8300 lbs. But my boat is heavy for the design - too many bells and whistles (but none I want to give up!).

As to launch and retrieval - I am 63 years old so no young buck and about 50% of the time I am taking it out solo. And I don't hesitate to do so. Yes, there was a learning curve but now that it is behind me I don't give it a second though. No it is not as easy as the Cabin Skiff but really no big deal.

But it all just does depend on what you want. The TG and the Double Eagle are both nice designs. But as you mentioned you might want to take a good look the the CS-20. I think it too could serve your mission well.
So Many Rivers,
So Little Time....

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Re: I/O weight for Double Eagle angle True Grit

Post by kens » Fri Feb 27, 2015 7:52 pm

Hey Ray, I can beat your numbers!!!
Dollar$ per Horsepower, a gas I/B can't be beat. You have a valid point that I/B has true axial driveline and the OB has to turn shaft around a 90' corner. I agree this is a talking point. But, the thing about drilling holes in the bottom is no big deal. It is a matter of workmanship and execution. Yeah, some I/B's are leaky, but not mine. Many besides me are not leaky. My shaft runs drip free, as does my rudder, and many other IB owners.
You say a I/B runs a bigger prop, that is true in many cases, but not all cases. The I/B has many more gear ratio choices than a OB or IO, by a wide and vast margin. A OB or IO comes with that gear ratio that you purchase, or purchase special racing gears for a Mercruiser IO (costly racing parts).
An I/B can be had with a common purchase ratio from different brands of tranny in 1:1 or 1.2:1 or 1.5:1 or 2.0:1 or 2.5:1 or 3:1, both axial inline or down angle or V-drive. The OB's cant do that. Funny thing is that all OB run approx a 1.8:1 gear ratio, and I have a 1,9:1. I got 80hp and turn a prop from 15x15 or 16x16 or 17x14. A 90hp OB with 1.8:1 gear aint turning any 15 dia at all. It just wont mount up. Why can I turn 16 dia and the OB wont? I dont know either. But it just that way.
The new technology OB are quiet, yes, but, so are the new technology IB. They got technology too. Too bad many of us take the dollars per horsepower to the extreme and run cheap old IB's. The new stuff is quiet too. You merely got to pony up the dollars. It is not a IB issue, it is a cheap homebuilder issue.
Have you seen a Nordhavn Trawler pull up to the dock? How about a 90' Viking? The Viking has a PAIR of 1,000hp diesels and pulled up to the dock as quiet as your True Grit. It's all about execution and workmanship.
And you have executed the True Grit quite well. I especially like the White oak trim with white paint, very nice.
Oak is over rated, everything about it takes extra time; then it warps, splits or checks !!! :roll:

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